ssl_adapter.py: Properly fix order of imports

A system running RDO Kilo (on EL 7) has the following two relevant
packages installed:
 python-requests --> /usr/lib/python2.7/site-packages/requests
 python-urllib3 --> /usr/lib/python2.7/site-packages/urllib3

The SSL Adapter in contrail-controller/src/config/common/ssl_adapter.py
gets installed as
/usr/lib/python2.7/site-packages/cfgm_common/ssl_adapter.py .

When using SSL against Keystone v3 from the contrail-api, that uses this
code, on a system such as the above, there will be a class loader type
bug, due to a incorrect order of imports in ssl_adapter.py.

The intended ImportError doesn't happen, since the native urllib3
actually exists, which leads to a mixup of name space between
the Pool Manager and the requests code, when executing.

The proper fix is to reverse the order of the imports, and have the
fallback become the base case.
Any non-RDO system will trigger the ImportError, and load the module
the regular way. And an RDO-based system works, as well.

Change-Id: Iba275c3521b1cdde5595fa443b449fdd962286fb
Closes-Bug: 1528851

src/config/common/ssl_adapter.py

@@ -1,19 +1,25 @@
+""" HTTPS Transport Adapter for python-requests, that allows configuration of
+    SSL version"""
 # -*- coding: utf-8 -*-
 # vim: tabstop=4 shiftwidth=4 softtabstop=4
 # @author: Sanju Abraham, Juniper Networks, OpenContrail
 from requests.adapters import HTTPAdapter
 try:
-    from urllib3.poolmanager import PoolManager
-except ImportError:
-    # This is required for redhat7 as it does not have
-    # separate urllib3 package installed
+    # This is required for RDO, which installs both python-requests
+    # and python-urllib3, but symlinks python-request's internally packaged
+    # urllib3 to the site installed one.
     from requests.packages.urllib3.poolmanager import PoolManager
-import ssl
+except ImportError:
+    # Fallback to standard installation methods
+    from urllib3.poolmanager import PoolManager
 
 class SSLAdapter(HTTPAdapter):
-    '''An HTTPS Transport Adapter that can be configured with SSL/TLS version.'''
+    '''An HTTPS Transport Adapter that can be configured with SSL/TLS
+       version.'''
+
     def __init__(self, ssl_version=None, **kwargs):
         self.ssl_version = ssl_version
+        self.poolmanager = None
 
         super(SSLAdapter, self).__init__(**kwargs)