Feature/fix test output parsing

These changes improve the parsing of the test output and fixes issue https://github.com/openbakery/gradle-xcodePlugin/issues/101

First, every command run through the command runner is now run via "script" which ensures that the stdout is line-buffered.  This fixes issues I was having with stdout and stderr being in the wrong order and sometimes resulting in partial lines of standard out.

Then I updated the test output parsing (of both XcodeTestTask and TestBuildOutputAppender) to look for the `** TEST SUCCEEDED **` or `** TEST FAILED **` that is output via xcodebuild's stderr stream at the end of a test run.  This is a much more reliable method for determining when each test destination run is complete.