Suppress nfs' file protocol from being published

The dcache-info-provider publishes all doors as endpoints by default. A
couple of doors are already configured to be excluded from this, but the
nfs door isn't and causes an file://xyz/ endpoint to be published.

Ticket: 8365
Acked-by:
Target: master
Request: 2.9
Request: 2.6
Request: 2.2
Require-book: no
Require-notes: yes
Merge pull request #680 from kschwank/2.6

Suppress nfs' file protocol from being published