tests: make simple single quotes work with dummyssh on windows

Mercurial assumes that the shell on remote servers over ssh servers uses unix
quoting rules. Tests using dummyssh are however also run on windows where cmd
doesn't parse single quotes like on unix.

This hack replaces the single quotes with double quotes on windows - that is
enough to make test-ssh.t pass after d8fa35c28335.

tests/dummyssh

@@ -16,5 +16,9 b' for i, arg in enumerate(sys.argv[1:]):'
     log.write(" %d:%s" % (i+1, arg))
 log.write("\n")
 log.close()
-r = os.system(sys.argv[2])
+hgcmd = sys.argv[2]
+if os.name == 'nt':
+    # hack to make simple unix single quote quoting work on windows
+    hgcmd = hgcmd.replace("'", '"')
+r = os.system(hgcmd)
 sys.exit(bool(r))