Fixes: 209: introduce SERF_RPC_ADDR to do the same as -rpc-addr

[lalyos]

No description provided.

[ryanuber]

Maybe the command-line args should take precedence over the environment. Might be confusing to see serf agent -rpc-addr=... in the process table but actually having a different address in use. Command line args also take precedence over config files. Other than that, LGTM.

[mitchellh]

Agree with @ryanuber, otherwise LGTM

[lalyos]

@ryanuber you're right, command-line args should take precendence.

Something is strange with travis:

I did the change, and was surprised by failing travis, so I

• I tested my changes in via crosbymichael's golang docker image and tests passed
• i pushed the code into github, and travis failed
• then by checking that travis uses tip go version, i explicitly set 1.2.1 and travis passed
• than changed back to tip and travis .. passed

maybe the tests has some raceconditions?

[ryanuber]

@lalyos Serf does have a bit of trouble with operations that involve timing while running the tests under travis CI. This has gotten a bit better over the last few months but can still be a little unpredictable. Your changes look good. Thanks!