kola: Refactor testiso tests

 - This is an initial step in order to try to merge kola tests and testiso,
much more work will be needed to create a final solution. Nonetheless,
for now let's start by breaking the tests and adding the same denylist
for both.

 - kola testiso now allows:
   - multipath, 4k, iso, pxe and firmware explicit tests;
   - Denylist for the pattern above and by test.
   Example:
    Add the following patterns in `kola-denylist.yaml` to deny it:
    - pattern: iso-as-disk.*
    - pattern: iso-as-iso-live-login.*.4k
    - pattern: iso-offline-install.ppcfw.*

Signed-off-by: Renata Andrade Matos Ravanelli <[email protected]>