Return early if v1 cgroups are not mounted
Return early if v1 cgroups are not mounted

on warden the nats fw feature breaks the agent start with

`2022-03-15_22:58:56.43738 [main] 2022/03/15 22:58:56 ERROR - Agent exited with error: Running bootstrap: Setting up networking: Setting up Nats Firewall: Error setting up cgroups for nats api access: cgroups: cgroup mountpoint does not exist`

add check if cgroups are mounted to the if that handles early returns.

cloudfoundry/bosh-agent,cloudfoundry/bosh-agent