Refactor osdetect for rhel family OSes

[fabi200123]

This PR refactors the osdetect for the OSes that are RHEL related. It adds a common.py where the detect_os_from_os_release is defined to return the proper info from /etc/os-release:

    return {
        "os_type": constants.OS_TYPE_LINUX,
        "distribution_name": distribution_name,
        "release_version": version,
        "friendly_release_name": "%s Version %s" % (
            distribution_name, version)}

NOTE: Due to the use of /etc/os-release, which was introduced starting with OSes like RedHat version 7 (e.g. RHEL 7, CentOS 7, OL7), this implementation makes the previous RedHat version 6 OSes to not work with the current logic for detecting OSes.

[petrutlucian94]

RHEL 6 and derivate OS-es do not have the /etc/os-release file. Are we going to drop RHEL 6 support? If so, the PR description must clearly state it. We can also remove RHEL 6 specific os-morphing code.

[fabi200123]

Left a NOTE in the PR description mentioning the /etc/os-release was added starting Redhat version 7, anything before not having it and thus the logic not working for them.