Do not fail when subnet is reserved

The reservation of subnets happening in cls method when two tests
run concurrently races may happen. Do not fail when subnet is reserverd
if we wanted to reserve it as it is okay and what we wanted.

Related-Prod: PRODX-36778
Change-Id: I0f35f0783430565f1886b710e33f991559fc7761
(cherry picked from commit 214943d4d8cf87b5e9d8f64481df725401e40c7b)
1 file changed