xrootd,pool: Fix xrootd and http logging context

Several executors didn't use a CDC resetting executor, causing the CDC
to be from whatever transfer first created the thread.

Target: trunk
Request: 2.11
Request: 2.10
Require-notes: yes
Require-book: no
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: https://rb.dcache.org/r/7507/