doors: Fix race condition in registration of mover creation and termination

The race condition caused srmCopy transfers to hang randomly.

Target: trunk
Require-notes: yes
Require-book: no
Request: 2.6
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6178/
(cherry picked from commit 9f63e72d05e275456295171c021bd61155c4d582)
Merge pull request #257 from gbehrmann/fix/2.6/rb6178

doors: Fix race condition in registration of mover creation and terminat...