oeqa.utils.metadata: fix retrieval of git branch and revision
Always return a valid branch name, or, '(nobranch)' if the current HEAD
is detached. Also, always return the hash of the commit object that HEAD
is pointing to. Previous code returned an incorrect branch name (or
crashed) e.g. in the case of detached HEAD.
[YOCTO #10590]
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
