Gitlab CI: enable triggering of dependent builds on Travis

Created by: mkszuba

Description

Extend .gitlab-ci.yml so that ensembl pipelines on EBI GitLab can trigger dependent builds in projects still using Travis.

Use case

The switch from to GitLab CI is to take place on a per-team basis so there will be dependent projects on Travis.

Benefits

Ensure CI compatibility of Core projects on EBI GitLab with dependent projects still on Travis.

Possible Drawbacks

In order for all dependent builds to be triggered successfully the user whose API token is used to authenticate with Travis REST API must have write access to all dependent repositories, which will have to be set up manually (in case of all-Travis runs there is implicit organisation-wide trust).

Testing

Have you added/modified unit tests to test the changes?

No.

If so, do the tests pass/fail?

N/A

Have you run the entire test suite and no regression was detected?

N/A, changes only affect the running of tests on EBI GitLab.