Allow skel.GENtoEVGEN.py to print platform

Print platform from skel.GENtoEVGEN.py so that we can identify in mcjoboptions the proper container that needs to be set up in the CI.

Might also be useful for other tests.

I have tested and see in the printout

10:38:47 Py:Gen_tf            INFO .platform = Linux-3.10.0-1160.99.1.el7.x86_64-x86_64-with-glibc2.17

AL9 would have .el9. in the name

@ewelina I added alsoTargeting:21.6 to keep things consistent - strictly speaking it's not necessary and in principle we could remove it.