Use olso.log directly

As the openstack/common is deprecated, Watcher should use oslo lib
directly to run in the openstack env. So there is much work to do
with oslo. This patch fixed the log part.

Change-Id: I3145a842fe3a22b3d08fec60d180329073edd50f

watcher/common/exception.py

@@ -23,11 +23,12 @@ SHOULD include dedicated exception logging.
 """
 
 from oslo_config import cfg
+from oslo_log import log as logging
+
 import six
 
 from watcher.common.i18n import _
 from watcher.common.i18n import _LE
-from watcher.openstack.common import log as logging
 
 LOG = logging.getLogger(__name__)