Support self signed SSL certificates when accessing Git repositories

com.atlassian.bamboo.repository.RepositoryException: https://git-server/my-repo/repo.git: cannot open git-upload-pack
	at com.atlassian.bamboo.plugins.git.GitOperationHelper.obtainLatestRevision(GitOperationHelper.java:90)
	at com.atlassian.bamboo.plugins.git.GitRepository.collectChangesSinceLastBuild(GitRepository.java:130)
	at com.atlassian.bamboo.v2.trigger.DefaultChangeDetectionManager.collectChangesSinceLastBuild(DefaultChangeDetectionManager.java:92)
 ....
Caused by: org.eclipse.jgit.errors.TransportException: https://git-server/my-repo/repo.git: cannot open git-upload-pack
	at org.eclipse.jgit.transport.TransportHttp.connect(TransportHttp.java:393)
	at org.eclipse.jgit.transport.TransportHttp.openFetch(TransportHttp.java:203)
	at com.atlassian.bamboo.plugins.git.GitOperationHelper.obtainLatestRevision(GitOperationHelper.java:72)
	... 22 more
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at com.sun.net.ssl.internal.ssl.Alerts.getSSLException(Alerts.java:174)
	at com.sun.net.ssl.internal.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1611)
....
	... 24 more
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:294)
....
	... 38 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target