Medium: exportfs: Make unlock_on_stop_default=1 (bnc#864263)

The resource agent should really release all locks which the NFS server
holds when stopping the resource. When this option was introduced, the
default was kept as 0 for compatibility reasons with legacy kernels,
existing users and non-Linux systems.

This is a proposal to make 1 the default. In most cases, this is the
desired behavior, and not setting this option can lead to unexpected
failures.

Original changeset that introduced this parameter: 612559c9