Do not require provisioning lock for tier2 deletion

The tier2 GC currently requires lock which is used by provisioning also. Due to the amount of provisionings run this might lead to very long time between tier2 GC acquiring the lock. This can lead to tier2 storage filling.

Only reason for the lock seems to be the to protect images that are being provisioned. Naming convention could be used to protect the in progress images instead of needing the lock.