run-tests: use different chg socket directories for different tests Before this patch, if --chg or --with-chg is specified, all tests are using the same chgserver socket. Since the chg client holds a lock when it starts a new server, and every test needs at least a new chg server due to different HGRCPATH affecting the confighash, the result is a lot of tests will be timed out if -j is large (for example, 50 or 100). This patch solves the issue by using different chg socket directories for different tests.