Run functional testsuite for PR builds

[dahorak]

Related to #6.

We would like to be able to install cluster and run functional test suite for every PR before it will be merged.

Intended workflow would be:
Once PR will be ready for merge, somebody will manually trigger test job for the respective PR

• The job will be triggered via comment run tests in the respective PR
• ❔ It might be possible to somehow specify dependencies on PRs from other repos (probably in the PR description or the run tests... comment).

[dahorak]

@TimothyAsir @nthomas-redhat @r0h4n would it make sense to specify dependencies on PRs from other repos this way:

Depends on: tendrl-ui/pr809 tendrl-notifier/pr153

either in the PR description or in the comment triggering the test execution (or both)?

It has to be on one line without any additional formating and has to follow quite precisely this format, to be able to correctly (and easily) parse it.
Basically the line has to start with depends on: string (case insensitive) followed by space separated list of dependencies in the form of: <reponame>/pr<id>, where <reponame> is the name of the repository (including tendrl- prefix) and <id> is the PR number.