run-tests.py: use --prefix instead of --home

Some SUSE version don't like --home, they fail with:
"error: must supply either home or prefix/exec-prefix -- not both"

this is due to SUSE shipping a distutils.cfg conflicting with --home.

tests/run-tests.py

@@ -176,7 +176,7 b' def install_hg():'
     # Run installer in hg root
     os.chdir(os.path.join(os.path.dirname(sys.argv[0]), '..'))
     cmd = ('%s setup.py clean --all'
-           ' install --force --home="%s" --install-lib="%s"'
+           ' install --force --prefix="%s" --install-lib="%s"'
            ' --install-scripts="%s" >%s 2>&1'
            % (sys.executable, INST, PYTHONDIR, BINDIR, installerrs))
     vlog("# Running", cmd)