run-tests: fix TESTDIR if testdescs are absolute paths Commit a18eef03d879 made TESTDIR be the location of the arguments that were passed to run-tests.py instead of just PWD. It assumed that these tests were specified using relative paths, so if pwd was /tmp/foo, and the first argument was /tmp/baz, it would set TESTDIR to /tmp/foo//tmp/baz. Differential Revision: https://phab.mercurial-scm.org/D1433