Add a command to generate a .travis.yml from user supplied parameters

[agrare]

Creating a .travis.yml file to run cross_repo tests is not user friendly. To simplify the process of creating a pull request on cross_repo-tests we can have a helper script that will build up a .travis.yml file which will run the tests properly.

This can include some user-friendly "buckets" for common use-cases like "test all providers" and "test UI and API".

Possible interface:

# Bucket for all providers
manageiq-cross_repo generate-travis-yml --repos=manageiq#1234,manageiq-schema#5678 --test=@all_providers

# Bucket for UI and API
manageiq-cross_repo generate-travis-yml --repos=manageiq#1234,manageiq-schema#5678 --test=@ui_and_api

# Manually specify the repos to test
manageiq-cross_repo generate-travis-yml --repos=manageiq#1234,manageiq-schema#5678 --test=manageiq-providers-amazon,manageiq-smartstate

# Mix buckets and specific repos
manageiq-cross_repo generate-travis-yml --repos=manageiq#1234,manageiq-schema#5678 --test=@all_providers,manageiq-smartstate

The output of this will be a .travis.yml file which can be committed to manageiq-cross_repo-tests so that a pull request can run the requested tests.

Eventually this can be used by miq-bot to enable this to be called by users from github comments. The interface/bucket-name here should match what is expected to be exposed by miq-bot.

[Fryguy]

Probably can steal some of this from ManageIQ/miq_bot#454

[cben]

If the interface is to be used in @miq-bot sentences, better avoid @ character in bucket names?