dcap: refactor PnfsSessionHandler to unify permission check and url handling

fixes issue with permission check with prestage over mounted NFS

Acked-by: Gerd Behrmann
Target: master, 2.11, 2.10
Ticket: #8518, #8532
Require-book: no
Require-notes: no
(cherry picked from commit 14d25b218f633eeba2bb18dcfcebd1d9d3c7f8e0)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
dcap: check for url in some commands

some dcap commands can be executed only with URL suntax

Acked-by: Gerd Behrmann
Target: master, 2.11, 2.10 ( in cobmination with 14d25b2)
Require-book: no
Require-notes: no
(cherry picked from commit fdb056cbc50f4455aba095fe2b5f08643b08d1f4)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #1104 from kofemann/fix-dcap-prestage-2.10

dcap: refactor PnfsSessionHandler to unify permission check and url hand...