Correct attribute referenced for Layer2 check. bnc#887238

There used to be install.inf's  attributes name conversion. It was
removed in patch starting at dffed1af505f81a4a6f0e1b51ee9d2f81504bb8a

An old hash key was referenced here.
Updated changelog
Updated testsuite
Merge pull request #233 from mchf/bnc887238-installation-HWAddr

s390: store mac address provided by user during installation