run-tests: set --home when building with distutils

If home was set in ~/.pydistutils.cfg, the tests could not run. This
overrides any home setting by supplying --home="" on the command line.

tests/run-tests.py

@@ -293,7 +293,7 b' def installhg(options):'
     os.chdir(hgroot)
     cmd = ('%s setup.py %s clean --all'
            ' install --force --prefix="%s" --install-lib="%s"'
-           ' --install-scripts="%s" >%s 2>&1'
+           ' --install-scripts="%s" --home="" >%s 2>&1'
            % (sys.executable, pure, INST, PYTHONDIR, BINDIR, installerrs))
     vlog("# Running", cmd)
     if os.system(cmd) == 0: