httppeer: use %s for formatting
This prevents a b'' from appearing in Python 3 output. We keep the
single quotes for backwards compatibility.
Differential Revision: https://phab.mercurial-scm.org/D5647
tests: add b'' to notcapable
This fixes some exceptions in a few tests.
# skip-blame just b'' prefixes
Differential Revision: https://phab.mercurial-scm.org/D5646