Delete sample changelog at end of test - check for open file leak

JENKINS-20585 reports that changelog.xml cannot be deleted on Windows
because it is held busy by a process.  This test assumes that process
is Jenkins itself, and that the GitChangeLogParser.parse() method is
the most likely culprit.
Changed to allow creating RevisionParameterAction using existing Revision, from a previous build for example. This provides the sha1, branches, etc. as they exist in the Revision for the parameter action on the new build.
Merge pull request #182 from daldinger/RevParms

Changed to allow creating a RevisionParameterAction using an existing Revision
Merge remote-tracking branch 'upstream/master'