Only conditionally import working keyring

keyring is conditionally imported if available on your platform,
however not all versions of keyring actually work. Specifically
we have global-requirements of >=2.1,!=3.3, so we know those are
the only versions we believe work.

If you are on an older platform, using system installed
python-keyring, python-keystoneclient won't install a new version,
because it's optional, but then will use a terriblely old verison,
which explodes with dbus errors.

The fix is to be more explicit on import.

Change-Id: I040f7b2311d7d5a450b8b12642752ac519b206fa
Closes-Bug: #1242992

keystoneclient/httpclient.py

@@ -20,14 +20,26 @@ OpenStack Client interface. Handles the REST calls and responses.
 """
 
 import logging
+import pkg_resources
 
 from six.moves.urllib import parse as urlparse
 
 try:
     import pickle
 
+    # NOTE(sdague): The conditional keyring import needs to only
+    # trigger if it's a version of keyring that's supported in global
+    # requirements. Update _min and _bad when that changes.
+    keyring_v = pkg_resources.parse_version(
+        pkg_resources.get_distribution("keyring").version)
+    keyring_min = pkg_resources.parse_version('2.1')
+    keyring_bad = (pkg_resources.parse_version('3.3'),)
+
+    if keyring_v >= keyring_min and keyring_v not in keyring_bad:
         import keyring
-except ImportError:
+    else:
+        keyring = None
+except (ImportError, pkg_resources.DistributionNotFound):
     keyring = None
     pickle = None