Accept IOException from temporaryDirectoryAllocator, don't fail test

The previous code checked for a Jenkins specific exception, but JDK 8
(or newer Jenkins versions needed for JDK 8) throw a standard Java
IOException rather than the Jenkins specific IOException2.
[Fix JENKINS-22343] JGit now shows first revision in repo correctly

The first revision in the repository has no parent.  The code assumed
all commits have at least one parent.
Add GitTool test