Replace Travis with GitHub Actions

[asbjornu]

Proposed Changes

This PR repalces Travis CI with GitHub Actions. Fixes the Linux part of #934. We need to figure out a way to bootstrap RabbitMQ on Windows in GitHub Actions, as that can't be done with Docker (within the same job, at least).

Types of Changes

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

[pivotal-issuemaster]

@asbjornu Please sign the Contributor License Agreement!

Click here to manually synchronize the status of this Pull Request.

See the FAQ for frequently asked questions.

[pivotal-issuemaster]

@asbjornu Thank you for signing the Contributor License Agreement!