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
Low: exportfs: Note caveats for unlock_on_stop in longdesc

Add note on limitations of unlock_on_stop on systems where
/proc/fs/nfsd/unlock_filesystem is not available.
Low: exportfs: Improved longdesc for unlock_on_stop
Merge pull request #394 from krig/unlock_by_default

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