This adds base_services_start handling for ARM. There are two problems
this DR solves. First is that we can't really use HDD_1_DECOMPRESS_URL for posting,
because it overwrites HDD_1 set in consecutive test. We use rather ugly hack that
we set HDD_2_DECOMPRESS_URL instead, set NUMDISKS=1, HDD_1=%HDD_2% for first
test and HDD_1 correctly for second test, see https://github.com/os-autoinst/openQA/issues/684.
Second problem is that in Base test matrix, tests are partitioned by subvariant,
ARM being exception. This introduces new "report variable" $SUBVARIANT_OR_ARM$.
the word "it" is wrong here, I think. Do you mean "Let's connect it as second HDD"?