Stop exception log in Big Switch unit tests
Stop exception log in Big Switch unit tests

Reduce unit test log sizes by removing stack trace
exception logging in Big Switch unit tests.

Closes-Bug: #1370898
Change-Id: Id808edb5db567db31b6c1366e20948683f20118a

openstack/networking-bigswitch,stackforge/networking-bigswitch,wolverineav/networking-bigswitch,wolverineav/networking-bigswitch,stackforge/networking-bigswitch,openstack/networking-bigswitch