Change Unix default server.id to be unique to support remote depots
and P4AUTH. This default is a defacto standard, and thus using a
more unique value should be promoted.
Optionally, we may want a truly unique identifier, e.g.
master.${SDP_INSTANCE}.${SOME_UUID}. Given that many SDP instances
in the wild use the default instance name of '1', and the
frequency of cororate mergers, the SDP_INSTANCE may not be unique
enough. But remote depots and P4AUTH are infrequently used.