SKIP_JCK_GIT_UPDATE do not prevent the existence of JCK_GIT_REPO

[judovana]

It seems the SKIP_JCK_GIT_UPDATE was not finished/was single usage targeted/or was broken in later commits.

Even if SKIP_JCK_GIT_UPDATE is set, and JCK_ROOT contains valid test materials, the JCK_GIT_REPO is verified and if set then used (if not then the run is interrupted). In worst scenario, it can even remove JCK_ROOT

If SKIP_JCK_GIT_UPDATE is set, and JCK_ROOT exists, then JCK_GIT_REPO should not be verified, and should not be used
Not sure waht to do if SKIP_JCK_GIT_UPDATE is set, and JCK_ROOT do not exists. It should then fail I guess.

#5740