do not try to lookup SHA1 from tags in planex-pin

[edwintorok]

The tag may not be a tag at all, but a commit hash, in which case the
bitbucket lookup would fail.

We do not need to perform the sha1 lookup for planex-pin, so avoid it instead of throwing a 404.

Signed-off-by: Edwin Török edvin.torok@citrix.com

[edwintorok]

Although I think planex-clone would still fail.

Traceback (most recent call last):
  File "/usr/bin/planex-clone", line 9, in <module>
    load_entry_point('planex==4.3.1', 'console_scripts', 'planex-clone')()
  File "/usr/lib/python2.7/site-packages/planex/cmd/clone.py", line 492, in main
    resources['PatchQueue0'])
  File "/usr/lib/python2.7/site-packages/planex/cmd/clone.py", line 332, in clone_with_patchq
    apply_patchqueue(base_repo, pq_repo, pq_res.prefix)
  File "/usr/lib/python2.7/site-packages/planex/cmd/clone.py", line 303, in apply_patchqueue
    base_repo.active_branch.name)
  File "/usr/lib/python2.7/site-packages/git/repo/base.py", line 631, in active_branch
    return self.head.reference
  File "/usr/lib/python2.7/site-packages/git/refs/symbolic.py", line 258, in _get_reference
    raise TypeError("%s is a detached symbolic reference as it points to %r" % (self, sha))
TypeError: HEAD is a detached symbolic reference as it points to '136c25bbb8d1424fc63764abba380654c7f70e66'