Improve release tag push

Both an improvement and a fix:

• push only the created tag instead of all local tags
• fix a strange issue making the tag being ignored

IT-release-on-demand-build-jdk6/nuxeo$ git push -n --tags
Everything up-to-date
IT-release-on-demand-build-jdk6/nuxeo$ git push -n --tags origin 
To git@github.com:nuxeo/nuxeo.git
 * [new tag]         jenkins-IT-release-on-demand-build-jdk6-20 -> jenkins-IT-release-on-demand-build-jdk6-20
 * [new tag]         release-5.6.0-HF31 -> release-5.6.0-HF31

=> it seems the remote name is now (since a Git upgrade?) required in some undefined cases.
Anyway, using explicit "git push origin release-5.6.0-HF31" instead is fixing the issue and a good improvement already applied in 5.9.1 (NXP-12643).