jqueue: convert to a SharedLock()
jqueue: convert to a SharedLock()

Remove the jqueue _lock member and convert to a _big_jqueue_lock
sharedlock. This allows smooth transition from the old single lock to a
more granular approach.

Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

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