[y][epic] Extend yast clients coverage in first boot tests
As of now we cover only yast clients which are enabled by default.
Motivated by https://trello.com/c/WN7ywJhr/1943-2-sles15-sp2-p3-1173298-yast2-firstboothostname-breaks-with-error and https://bugzilla.suse.com/show_bug.cgi?id=1173298
Here we can see full list of available clients: https://github.com/yast/yast-firstboot/blob/master/control/firstboot.xml
There is refactoring of the first boot functionality planned, so we should clarify the requirements.
All the clients cannot be enabled in one test suite as some of them conflict with each other, so we will need to split it to multiple scenarios.
See for the reason of tracker change: http://mailman.suse.de/mailman/private/qa-sle/2020-October/002722.html