Fix the issue where persistent DVS is used to run pytest

and ports are created dynamically (ref pr:
sonic-net/sonic-buildimage#4499). There were two
issues:

a) since number of dynamic front port can be < 32 test case fails
   as it expect always 32. Make sure to udpate persitent DVS to always have
   32 ports/server link as part of test run and save the current config
   db

b) after test is done persistent DVS need to be moved to original state.
   Make dure to remove extra port/server link and restore back config db

Signed-off-by: Abhishek Dosi <[email protected]>

tests/conftest.py

@@ -193,6 +193,7 @@ def __init__(self, name=None, imgname=None, keeptb=False, fakeplatform=None):
             self.cleanup = False
         else:
             self.cleanup = True
+        self.persistent = False
         if name != None:
             # get virtual switch container
             for ctn in self.client.containers.list():
@@ -203,7 +204,9 @@ def __init__(self, name=None, imgname=None, keeptb=False, fakeplatform=None):
                     else:
                         (status, output) = subprocess.getstatusoutput("docker inspect --format '{{.HostConfig.NetworkMode}}' %s" % name)
                     ctn_sw_id = output.split(':')[1]
+                    # Persistent DVS is available.
                     self.cleanup = False
+                    self.persistent = True
             if self.ctn == None:
                 raise NameError("cannot find container %s" % name)
 
@@ -227,6 +230,10 @@ def __init__(self, name=None, imgname=None, keeptb=False, fakeplatform=None):
             self.mount = "/var/run/redis-vs/{}".format(ctn_sw_name)
 
             self.net_cleanup()
+            # As part of https://github.com/Azure/sonic-buildimage/pull/4499
+            # VS support dynamically create Front-panel ports so save the orginal
+            # config db for persistent DVS
+            self.runcmd("mv /etc/sonic/config_db.json /etc/sonic/config_db.json.orig")
             self.ctn_restart()
         else:
             self.ctn_sw = self.client.containers.run('debian:jessie', privileged=True, detach=True,
@@ -271,7 +278,13 @@ def __init__(self, name=None, imgname=None, keeptb=False, fakeplatform=None):
     def destroy(self):
         if self.appldb:
             del self.appldb
-        if self.cleanup:
+        # In case persisten dvs was used removed all the extra server link
+        # that were created
+        if self.persistent:
+            for s in self.servers:
+                s.destroy()
+        # persistent and clean-up flag are mutually exclusive
+        elif self.cleanup:
             self.ctn.remove(force=True)
             self.ctn_sw.remove(force=True)
             os.system("rm -rf {}".format(self.mount))
@@ -1043,6 +1056,10 @@ def dvs(request):
     else:
         dvs.get_logs()
     dvs.destroy()
+    # restore original config db
+    if dvs.persistent:
+        dvs.runcmd("mv /etc/sonic/config_db.json.orig /etc/sonic/config_db.json")
+        dvs.ctn_restart()
 
 @pytest.yield_fixture
 def testlog(request, dvs):