Deprecate the --keep-rhsm option and stop uninstalling subscription-mananager

We can make the --keep-rhsm option deprecated and never uninstall the installed sub-man packages.

And instead of uninstalling them, we can reinstall/update them with the RHEL ones to ensure that they are up-to-date and work well because we are testing the conversion with the RHEL sub-man packages. For example the subscription-manager-rhsm-certificates package available in CentOS Linux 7 repos is missing the /etc/rhsm/ca/redhat-uep.pem certificate and without it it's not possible to register to Red Hat Candlepin/subscription.rhsm.redhat.com. The reinstall/update won't break the existing registration or subscription of the system.

Acceptance criteria

• convert2rhel never uninstalls the installed sub-man packages
• The --keep-rhsm option is marked as deprecated in man/help
• Install the /etc/rhsm/ca/redhat-uep.pem cert if missing (the sub-man from CentOS Linux 7 repos is missing the cert)
• This enhancement is released after or together with RHELC-1033 (no unregistering by default)

Notes:

• For now we'll not check if the installed sub-man packages are of an older version than those available in UBI (or the new uprotected CDN repo).
  • We can start updating it (with first backing it up) when we get a customer report about some issue with uing an older sub-man version