Check for gnt-cluster before running gnt-cluster upgrade
Check for gnt-cluster before running gnt-cluster upgrade

When ganeti is removed (not purged) `/etc/cron.d/ganeti` is not deleted,
thus after a reboot cron tries to execute gnt-cluster upgrade and fails.

The same pattern is used on all other cron entries.

Signed-off-by: Christos Trochalakis <28d52ccc67a38a0cc89b0627b1175cf65490a0ef@skroutz.gr>
Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

andir/ganeti,grnet/snf-ganeti,leshchevds/ganeti,yiannist/ganeti,yiannist/ganeti,bitemyapp/ganeti,ganeti/ganeti,mbakke/ganeti,andir/ganeti,ganeti/ganeti,grnet/snf-ganeti,andir/ganeti,leshchevds/ganeti,mbakke/ganeti,mbakke/ganeti,onponomarev/ganeti,bitemyapp/ganeti,leshchevds/ganeti,yiannist/ganeti,onponomarev/ganeti,ganeti/ganeti