dcap: convert ClosedByInterruptException into InterruptException

this prevents pools to disable by JTM or mover kill

Acked-by: Paul Millar
Target: master, 2.6
Require-book: no
Require-notes: no
(cherry picked from commit aaf19b4c88d023183daf0e409bfebf0eee848c39)
Merge pull request #242 from kofemann/fix-dcap-mover-2.6

dcap: convert ClosedByInterruptException into InterruptException