[vrouter_netns] Create netns if it's not exist

If the script opencontrail-vrouter-netns is call with the '--uptae'
flag, the Linux network namespace is not initialized before it sets SNAT
or LBaaS stuff on it. So it fails. To resolve that, it create it if it's
not exist.

Change-Id: I74f87f3e7f1ebca1ac664d646d139a4f6eddbf98
Closes-Bug: #1466879
(cherry picked from commit cc61f98)

src/vnsw/opencontrail-vrouter-netns/opencontrail_vrouter_netns/vrouter_netns.py

@@ -102,8 +102,7 @@ def create(self):
 
     def set_snat(self):
         if not self.ip_ns.netns.exists(self.namespace):
-            raise ValueError('Need to create the network namespace before set '
-                             'up the SNAT')
+            self.create()
 
         self.ip_ns.netns.execute(['sysctl', '-w', 'net.ipv4.ip_forward=1'])
         self.ip_ns.netns.execute(['iptables', '-t', 'nat', '-F'])
@@ -134,8 +133,7 @@ def set_snat(self):
 
     def set_lbaas(self):
         if not self.ip_ns.netns.exists(self.namespace):
-            raise ValueError('Need to create the network namespace before set '
-                             'up the lbaas')
+            self.create()
 
         haproxy_process.start_update_haproxy(self.cfg_file, self.namespace, True,
                                              self.keystone_auth_cfg_file)