[CHEF-2420] Support annotated tags in the git provider

Annotated tags have their own SHA and also point to a SHA in the git
repo. Using git ls-remote $REPO $TAG* the tagged SHAs can be
identified by the '^{}' suffix appended to the corresponding tag name.

When resolving the remote reference, we now search for $TAG* and use
the SHA of the tagged commit (with ^{}) if it is there and otherwise
use the SHA with an exact match for $TAG (to avoid capturing anything
extra via the glob used to return refs).

Also, if no revision is specified, we force 'HEAD' in the git
ls-remote call.