mesos_user_http_host

[dmitrypekar]

Hey,

This is first PR. It is required for two purposes:

• dev (need possibility to specify http host name);
• dcos compat (need possibility to specify framework user);

I've added support of following options:

• mesos_user - specifies framework user (defaults to "");
• host - specifies public address of http host (defaults to "localhost");

Both those options are required if running Scheduler outside of mesos hosts
(for instance when using vagrant for mesos and running Scheduler inside IDE).

Please review & merge.

[BenWhitehead]

Thanks @dmitrypekar