core upgrade does not upgrade all cores

[endorama]

Bug Report

Current behavior

Running arduino-cli core upgrade command does not perform core upgrade of all cores.

Expected behavior

As per its help text, I would expect it to "# upgrade everything to the latest version"

Environment

• CLI version (output of arduino-cli version): arduino-cli Version: 0.3.7-alpha.preview Commit: BuildDate: 2019-07-11 07:48:27.111552645 +0000 UTC
• Go version (if building from sources): go version go1.12.5 linux/amd64
• OS version: Ubuntu 16.04.6 LTS

The same issue seems to be present building latest master from source.

Additional context

To reproduce:

• arduino-cli core list
• arduino-cli core upgrade
• arduino-cli core list <= core still require updates

Debug output:

$ arduino-cli core list
ID           Installed Latest Name                                        
arduino:avr  1.6.23    1.6.23 Arduino AVR Boards                          
arduino:samd 1.6.22    1.8.3  Arduino SAMD Boards (32-bits ARM Cortex-M0+)
$ arduino-cli core upgrade --debug
INFO[0000] Checking for config file in: $HOME/.arduino15/arduino-cli.yaml 
INFO[0000] Checking if CLI is Bundled into the IDE      
INFO[0000] Candidate IDE Directory: $HOME/go/bin 
INFO[0000] CLI is not bundled into the IDE              
INFO[0000] Checking for config in: /arduino-cli.yaml    
INFO[0000] error loading                                 error="open /arduino-cli.yaml: no such file or directory"
INFO[0000] Checking for config in: /home/arduino-cli.yaml 
INFO[0000] error loading                                 error="open /home/arduino-cli.yaml: no such file or directory"
INFO[0000] Checking for config in: $HOME/arduino-cli.yaml 
INFO[0000] error loading                                 error="open $HOME/arduino-cli.yaml: no such file or directory"
INFO[0000] Configuration set                            
INFO[0000] arduino-cli-0.3.7-alpha.preview              
INFO[0000] Starting root command preparation (`arduino`) 
INFO[0000] Formatter set                                
INFO[0000] Initializing package manager                 
INFO[0000] Checking if CLI is Bundled into the IDE      
INFO[0000] Candidate IDE Directory: $HOME/go/bin 
INFO[0000] Loading hardware from: $HOME/.arduino15/packages 
INFO[0000] Loading package arduino from: $HOME/.arduino15/packages/arduino/hardware 
INFO[0000] Loaded platform                               platform="arduino:[email protected]"
INFO[0000] Loaded platform                               platform="arduino:[email protected]"
INFO[0000] Loaded platform                               platform="arduino:[email protected]"
INFO[0000] Checking existence of 'tools' path: $HOME/.arduino15/packages/arduino/tools 
INFO[0000] Loading tools from dir: $HOME/.arduino15/packages/arduino/tools 
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:arm-none-eabi-gcc@7-2017q4"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loaded tool                                   tool="arduino:[email protected]"
INFO[0000] Loading package builtin from: $HOME/.arduino15/packages/builtin 
INFO[0000] Checking existence of 'tools' path: $HOME/.arduino15/packages/builtin/tools 
INFO[0000] Loading tools from dir: $HOME/.arduino15/packages/builtin/tools 
INFO[0000] Loaded tool                                   tool="builtin:[email protected]"
INFO[0000] Loaded tool                                   tool="builtin:[email protected]"
INFO[0000] Adding libraries dir                          dir=$HOME/Arduino/libraries location=sketchbook
INFO[0000] Adding libraries dir                          dir=$HOME/.arduino15/packages/arduino/hardware/avr/1.6.23/libraries location=platform
INFO[0000] Adding libraries dir                          dir=$HOME/.arduino15/packages/arduino/hardware/samd/1.6.22/libraries location=platform
INFO[0000] Executing `arduino core upgrade`             
$ arduino-cli core list
ID           Installed Latest Name                                        
arduino:avr  1.6.23    1.6.23 Arduino AVR Boards                          
arduino:samd 1.6.22    1.8.3  Arduino SAMD Boards (32-bits ARM Cortex-M0+)

[masci]

Closed via #291