Changed so PROXY_TARGET value is consistently:
${SSL_PREFIX}${P4MASTERHOST}:${P4BROKERPORTNUM}
Reasons:
* The existing sample value always had to be changed, as the replacement
value REPL_P4P_TARGET_PORT was never substituted, requiring manual
setting when the proxy was added to a topology.
* Using the new value is a reasonable default, and promotes the idea
that proxies should point to the broker on the master host. (If
brokers are not used, it's an easy tweak to change P4BROKERPORTNUM
to P4PORTNUM.)