Need to fix vmvn testcase test_multistep_vm_add_delete_with_stop_start_service

The test case test_multistep_vm_add_delete_with_stop_start_service which is failing in regression.
Seen the issue while doing the below steps
1. vm2 is brought up when vrouter docker is stopped. So it was not coming up as expected.
2. Then vm2 came up after starting the vrouter docker.
3. Script is checking tap interface of the vm in the introspect agent

But it is not there in the introspect agent. Need to get an input from vrouter team and fix accordingly.