cmdlib._ReleaseLock: Do nothing if no locks are owned
cmdlib._ReleaseLock: Do nothing if no locks are owned

The locking library doesn't like it when “release()” is called on
a lockset or lock which isn't held by the current thread. Instead
of modifying the library, which could have other side-effects,
this rather simple change avoids errors when a LU simply tries to
release all locks, even when it doesn't own any at a certain level.

Signed-off-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

onponomarev/ganeti,grnet/snf-ganeti,yiannist/ganeti,ganeti/ganeti,mbakke/ganeti,mbakke/ganeti,ganeti/ganeti,apyrgio/ganeti,yiannist/ganeti,yiannist/ganeti,bitemyapp/ganeti,andir/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,dimara/ganeti,leshchevds/ganeti,bitemyapp/ganeti,dimara/ganeti,apyrgio/snf-ganeti,andir/ganeti,grnet/snf-ganeti,mbakke/ganeti,andir/ganeti,apyrgio/snf-ganeti,apyrgio/ganeti,leshchevds/ganeti,ganeti/ganeti