Add ability to specify worker in ramp-test submission

[jorisvandenbossche]

This works with the master branch of ramp-board (only ramp-engine and ramp-utils is needed).

The usage is like:

ramp-test --submission starting_kit_local2 --worker conda_config.yml 
# or
ramp-test --submission starting_kit_local2 --worker aws_config.yml 

where the configuration file then has the information about the worker.

TODO:

• add tests
• think about how this needs to interact with the other options to ramp-test, because currently they are not passed through.

[jorisvandenbossche]

Need to update this for the latest changes in ramp-board

[kegl]

Looks great! Yes, can't we just pass the other options to the ramp-test command that the worker executes?