Overwrite lock wait time with (optional) system property

Very useful/necessary if you have long running migrations (>5 min) in a cluster. Only one node performs the migration, other nodes are waiting and then end in a time out. Setting the system property e.g. liquibase.changeLogLockWaitTimeInMinutes=15 will increase wait time before the timeout kicks in.
Merge pull request #150 from romeop/next

Overwrite lock wait time with (optional) system property