common.sh: do not reload arduino when already present (for locally CI testing)

Author: d-a-v

tests/common.sh

@@ -104,7 +104,7 @@ function install_ide()
     local ide_path=$1
     local core_path=$2
     local debug=$3
-    wget -O arduino.tar.xz https://www.arduino.cc/download.php?f=/arduino-nightly-linux64.tar.xz
+    test -r arduino.tar.xz || wget -O arduino.tar.xz https://www.arduino.cc/download.php?f=/arduino-nightly-linux64.tar.xz
     tar xf arduino.tar.xz
     mv arduino-nightly $ide_path
     cd $ide_path/hardware