[Proposal] Add the possibility to configure Myriad with environment variables

[Juan P <jp...@gmail.com>]

Hello community, I would like to propose the possibility of adding a change
in the configuration process of the Myriad scheduler. Now the initial
configuration is static (with file) and can not adapt in an agile way to
the needs of different environments, or to the mechanisms of
meta-schedulers tools such as Marathon or Aurora.

I think it would be interesting to provide a configuration mechanism for
environment variables. Perhaps, maintaining a hierarchical order of
priority:
ENVIRONMENT_VARIABLE else FILE else DEFAULT_VALUE

In this way we could configure Myriad in deploy time in a simple way and
adapt the configuration for different environments deploying the same
artifacts.

What do you think?

Thank you