lib/oeqa/runtime: rewrite the systemd test module

lib/oeqa/runtime: rewrite the systemd test module

They are basically the same tests but:
- they look cleaner, using one single method / assert
- output from unittest will be cleaner (and includes a verbose status when needed)
- they are better grouped and use a real, active, enabled service
  (machineid will be dropped and hostnamed was a static service)

(From OE-Core rev: 0aa5b97f9e0d8941ce342e9f162dd3b19d4b49bb)

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>