Refactor Orchestra\Extension\Finder::registerExtension() which would reduce call to request and generate manifest config on each request.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.1' into 2.2
Remove PHP 5.6 from allow failures.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.1' into 2.2
Merge branch '2.2'