Fix VIP plug failure if netns directory exists

In rare cases, the network namespace may already exist in the amphroa.
VIP plug should not fail if the directory is already present.

Change-Id: I33c2e1740bff1313ba6b8d3ef2ea4fe494263751
Story: 2004300
Task: 27856
(cherry picked from commit 63b5cfc14e)

octavia/amphorae/backends/agent/api_server/osutils.py

@@ -12,6 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import errno
 import ipaddress
 import os
 import shutil
@@ -78,7 +79,13 @@ class BaseOS(object):
         # We need to setup the netns network directory so that the ifup
         # commands used here and in the startup scripts "sees" the right
         # interfaces and scripts.
-        os.makedirs('/etc/netns/' + consts.AMPHORA_NAMESPACE)
+        try:
+            os.makedirs('/etc/netns/' + consts.AMPHORA_NAMESPACE)
+        except OSError as e:
+            # Raise the error if it's not "File exists" otherwise pass
+            if e.errno != errno.EEXIST:
+                raise
+
         shutil.copytree(
             network_dir,
             '/etc/netns/{netns}/{net_dir}'.format(