Change repository name used in bootstrap tests

This changes the name of the repository that is used for the GitHub
end-to-end tests to a name that is still traceable to the source
(repository) that created it, by using the format
`<ORIGIN_REPOSITORY_NAME>-<PSEUDO_RAND_SUFFIX>`.

The `PSEUDO_RAND_SUFFIX` is a SHA1 sum of the name of the branch and
commit SHA the tests run for, resulting in a 40 character suffix that
unlike the short commit SHA used before, should not result in collisions.

Signed-off-by: Hidde Beydals <hello@hidde.co>