Add a try block while doing the purging
Add a try block while doing the purging

This is to work around an issue that a broken pipe exception
might get thrown when we invoke this purge through neutron
client API. We don't have this issue when its invoked thru
CLI.

Change-Id: I94d6ab8658efc08dd5be8dbd348e098453e71b39

noironetworks/python-group-based-policy-client,noironetworks/python-group-based-policy-client