Provide GIT_COMMIT_SHORT environment variable

GIT_COMMIT env variable provides SHA of the current commit being build.

Please also provide GIT_COMMIT_SHORT env variable that contains the short format of SHA that is easier to read and to use as build qualifier.

e.g. 81995adb1726ffdd1ab9c8911fe2bfa2a96f6679 would be shown as 81995ad

Links:
https://stackoverflow.com/questions/5694389/get-the-short-git-version-hash#answer-5694416

https://git-scm.com/docs/git-rev-parse