Fixed file permission issues for lbaas ssl certificates

ssl certificates are with 0644 file permission which is
changed to 0600

Change-Id: I4ac0c2305dc9f031ae578e9adcce4494dcc253b4
Closes-bug: #1710859

src/vnsw/opencontrail-vrouter-netns/opencontrail_vrouter_netns/cert_mgr/tls.py

@@ -42,4 +42,5 @@ def create_pem_file(self, dest_dir):
         f = open(pem_file_name, 'w')
         f.write(pem)
         f.close()
+        os.chmod(pem_file_name, 0600)
         return pem_file_name