set testing.ready when requesting retest
set testing.ready when requesting retest

testing.ready should be set not just when the git repository is
updated, but also when the user or API client requests a rerun.
This makes the method name 'remove_testing_properties' a bit
confusing, so rename it to 'clear_and_start_testing'.

patchew-project/patchew,patchew-project/patchew,patchew-project/patchew,patchew-project/patchew