tests: use readlink.py instead of readlink
The latter doesn't always exist, such as on Solaris-derived platforms.
Differential Revision: https://phab.mercurial-scm.org/D999
tests: use readlink.py instead of readlink
The latter doesn't always exist, such as on Solaris-derived platforms.
Differential Revision: https://phab.mercurial-scm.org/D998