added tests for issues_list an all providers

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added tests for issue_create and issue_delete on all providers

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added tests for accessing low-level providers on all providers

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>