Bug 15006: Centralize timeout logic and allow zero client timeout

Bug 15006: Centralize timeout logic and allow zero client timeout

Moving timeout logic to one routine (with unit test).

This further implements two suggestions from Kyle and Larry:

[1] You could use a client_timeout of 0 to specify no timeout at all.
[2] Have the client_timeout default to the timeout if not defined.

Test plan:
[1] Run t/db_dependent/SIP/SIPServer.t.
[2] Test login timeout for raw and telnet.
[3] Check ACS status message for timeout value. Should match policy
    timeout from institution.
[4] Test client timeout (zero and non-zero).
[5] Remove client timeout. Test fallback to service.
[6] Remove service timeout too. Test fallback to 30 at login.

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Amended to incorporate Srdjan's suggestion to move get_timeout to
SIPServer.pm; this requires some additional mocking in the unit test.
And even makes the test db dependent, as documented.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>