tests: restore 'python' and '$TESTDIR/' for dummyssh invocation This is a backout of 46727fea7a00, and a partial backout of c3ecbf694904. Windows won't execute 'dummyssh' directly, presumably because CreateProcess() doesn't know how to execute a bash script: $ hg clone -e "dummyssh" ssh://user@dummy/cloned sshclone remote: 'dummyssh' is not recognized as an internal or external command, remote: operable program or batch file. abort: no suitable response from remote hg! [255] With the restoration of python as the executable, $TESTDIR needs to be restored for these invocations, because python won't search $PATH for 'dummyssh': $ hg clone -e "python dummyssh" ssh://user@dummy/cloned sshclone remote: python: can't open file 'dummyssh': [Errno 2] No such file or directory abort: no suitable response from remote hg! [255]