loginbroker: Comply with new configuration policy

Drops the service srm-loginbroker. All doors now register with
a single login broker called LoginBroker and SRM and all
monitoring services query this one LoginBroker to locate doors.
SRM is updated to exclude srm as a transfer protocol, thus
making it safe to register all doors in the same login broker.

The dcache.service.loginbroker property is updated to take
a comma separated list of loginbrokers to register with or
to query. httpd now uses this property to configure which
loginbrokers to query.

New properties

loginbroker.cell.name
srm.protocols.disallowed.get
srm.protocols.disallowed.put
srm.protocols.preferred

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5742/