Typo fixed
[mce] Support for reconnecting to mce when it's gone

To test, start PackageKit as root user in verbose mode:

     /usr/libexec/packagekitd --verbose

In another session as root, stop mce temporarily:

     systemctl stop mce.service

In yet another session as user, ask PackageKit to do something:

     pkcon refresh

In the first session where packagekitd is running in verbose mode,
it will wait for mce to come back (and try evert 5 seconds to do so)
and print warnings while it fails. After restarting mce, PackageKit
can successfully connect to mce again:

     systemctl start mce.service