sidedata: adjust string for python3
This was pointed out by Gregory Szorc: Python 3 will require a r'' because of
source transformation.
Differential Revision: https://phab.mercurial-scm.org/D6968
py3: fix phabricator's use of json.loads() for py3.5
Missed this in
c340a8ac7ef3 since `loads()` takes bytes from 3.6 onwards.
Differential Revision: https://phab.mercurial-scm.org/D6961
run-tests: make coverage work out of tree
Currently coverage fails when run on an out-of-tree extension since
run-tests.py tries to load sitecustomize.py from self._testdir, which is the
dir for the extension's tests.
Differential Revision: https://phab.mercurial-scm.org/D6960