rpmbuild: add copr-builder-rhsm-subscribe script

[praiskup]

This allows us to specify RHSM password so it is not visible on ps aux output

[nikromen]

if this will be closed (not merged), we need to do the expect magic in fedora-infra/ansible

[praiskup]

Some new observations:

• the activation keys have a much smaller identity scope compared to passwords (we are not risking the loss of our identity, just that we give someone rights to enable new systems)
• the key is read from stdin so it is neither in /proc/self/comm nor in /proc/self/environ
• the daemon process that has the password in memory disappears relatively quickly, before we let the user in over ssh, unless there's a problem with RHSM
• because problems with RHSM happen "from time to time", we should count that /proc/self/mem analysis might lead to some leaks, so we should rotate the key (I doubt there's a huge motivation to do this, because getting RH Developer license is much easier).

[FrostyX]

This PR is probably blocked by the switch of our account to SCA, right?

[praiskup]

This PR is probably blocked by the switch of our account to SCA, right?

Not really, this can stay unused till we switch.