ls-remote to lookup references in a remote repository

List references, like heads or tags, in a remote repository
without depending on a locally cloned workspace.

The git-parameter plugin lists branches or tags on a local
cloned workspace, so it doesn't work on the first build or
if user wipes out workspace.

If user only wants a tag name with its commit id, there is
no need to clone the whole repository.
Merge pull request #150 from yestin/master

ls-remote to lookup references in a remote repository
Merge remote-tracking branch 'upstream/master' into proto-jdk8

Conflicts:
	src/main/java/org/jenkinsci/plugins/gitclient/RemoteGitImpl.java