[Config]: Fix physical router list
[Config]: Fix physical router list

API server crashes when physical router list func. gets called with
'physical-router' KeyError. Added a check for this key to be present in
the dict before reading it.

Change-Id: I178865ef383d239174bc947b48ea33c46d15b980
Closes-Bug: #1702245

eonpatapon/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,nischalsheth/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,eonpatapon/contrail-controller