Add a force option to push
added testcase for force push [JENKINS-24082]
Merge pull request #1 from wannessels/forceOption

added testcase for force push [JENKINS-24082]
Merge pull request #248 from guilhem/forceOption

[FIXED JENKINS-24082] Add a force option to push command
fixed GitPublisherTest.testForcePush , was not deterministic [JENKINS-24082]