[6.11.z] Parametrize KS repo syncing test

[Satellite-QE]

Cherrypick of commit: e07c0a322aae333e06f0b9c44a5c4c676c2b6ba2

This PR presents two changes:

1. Fixes md5_by_url method. The original one returned md5sum even when the file did not exist instead of raising error (sum of an empty output, same as md5sum /dev/null).
2. Parametrization for the three latest baseos KS repos.

[Gauravtalreja1]

trigger: test-robottelo pytest: tests/foreman/api/test_contentmanagement.py::TestCapsuleContentManagement::test_positive_sync_kickstart_repo