Allow tree-ish to be used for galaxy role version

Ensure that ansible-galaxy version can be a branch, a tag, or any tree-ish
supported by git including specific commit IDs.  For git scm roles, adds an
explicit git checkout of the specified role_version prior to the git archive.
This means that we'll always archive from HEAD of whatever role_version is
checked out. role_version can be a branch, a tag, or any <tree-ish> supported
by git including specific commit IDs.  These changes also ensure
ansible-galaxy works for scm clones when specified version differs from
repository default branch.

lib/ansible/galaxy/role.py

@@ -310,5 +310,3 @@ class GalaxyRole(object):
         }
         """
         return dict(scm=self.scm, src=self.src, version=self.version, name=self.name)
-
-

lib/ansible/playbook/role/requirement.py

@@ -190,6 +190,17 @@ class RoleRequirement(RoleDefinition):
         if rc != 0:
             raise AnsibleError ("- command %s failed in directory %s (rc=%s)" % (' '.join(clone_cmd), tempdir, rc))
 
+        if scm == 'git' and version:
+            checkout_cmd = [scm, 'checkout', version]
+            with open('/dev/null', 'w') as devnull:
+                try:
+                    popen = subprocess.Popen(checkout_cmd, cwd=os.path.join(tempdir, name), stdout=devnull, stderr=devnull)
+                except (IOError, OSError):
+                    raise AnsibleError("error executing: %s" % " ".join(checkout_cmd))
+                rc = popen.wait()
+            if rc != 0:
+                raise AnsibleError("- command %s failed in directory %s (rc=%s)" % (' '.join(checkout_cmd), tempdir, rc))
+
         temp_file = tempfile.NamedTemporaryFile(delete=False, suffix='.tar')
         if scm == 'hg':
             archive_cmd = ['hg', 'archive', '--prefix', "%s/" % name]