srm: Make login broker of SRM configurable and clean up properties

The patch allows the login brokers used by the SRM to be configurable.
Since the SRM uses two login brokers, one for lookup and one for
registration, I have renamed all related properties such that those
related to door lookup begin with srm.lookup. and those for login
broker registration begin with srm.loginbroker.

When merging into stable branches, the old properties will not be marked
deprecated.

Deprecated by this patch:

srmLoginBrokerUpdatePeriod
srmNumberOfDoorsInRandomSelection

Introduced by this patch:

srm.lookup.loginbroker
srm.lookup.timeout
srm.lookup.population-size
srm.loginbroker
srm.loginbroker.period
srm.loginbroker.threshold
srm.loginbroker.family
srm.loginbroker.version

Target: trunk
Request: 2.6
Request: 2.2
Require-book: yes
Require-notes: yes
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5604/