* cgv1: do not disable cpuset manager if reserved interface already exists
This PR fixes a bug where restarting a Nomad Client on a machine using cgroups
v1 (e.g. Ubuntu 20.04) would cause the cpuset cgroups manager to disable itself.
This is being caused by incorrectly interpreting a "file exists" error as
problematic when ensuring the reserved cpuset exists. If we get a "file exists"
error, that just means the Client was likely restarted.
Note that a machine reboot would fix the issue - the groups interfaces are
ephemoral.
* cl: add cl
Seth Hoenig