Missing information in Vulpix test logs

[nicolasstucki]

There is currently no way to inspect compiler logs after a failure or success of a test. This will become a blocker when we remove partest.

[felixmulder]

Gathering some more precise information in this issue:

• On failure, the logs are dumped for all failed tests by the summary report: SummaryReport.java
• The things that are dumped is everything from the test reporter's messageBuf courtesy of TestReporter#flushToFile
• All compiler errors and messages are added to the buffer here: TestReporter#printMessageAndPos

Things that are not dumped to file:

• Other prints to stderr

When things are not dumped to log:

• Zero failed tests

In #2194 we need to make sure of the following the fix these issues:

• Tests should all be using the reporter from TestSummary (everything printed to a single file by a single reporter)
• Should add some way to always dump all logs