In a DC env, when management network connectivity is disrupted
for some time, cert-mon's audit greenthreads hang. This
happens because of missing timeouts in REST API requests which
cause the urlopen to remain hanging forever. As a result, the
dc-cert sync status for the subcloud remains unknown
indefinitely and the subclouds remain out-of-sync.
This commit adds a timeout to the _get_token method to avoid
Signed-off-by: Jessica Castelino <email@example.com>