Add --instrepokey

This lets testers define the key that will be used to verify the
contents of instrepo when they're using a custom instrepo.

Related: rhbz#1115532
Related: rhbz#1123915

(cherry picked from commit d0c6353692e40a61bac5a28f23c6d98e6b2c60bc)
Automatically add the GPG key to Red Hat repos.

Resolves: rhbz#1123915
Revert "fetch/verify .treeinfo.signed if gpgcheck is on"

This reverts commit 1dcb74d5b8e83e9b54544e23090bc30b4a34a681.

Red Hat Enterprise Linux does not use treeinfo.signed, so skip this
check.

Related: rhbz#1123915
Cleanup repo files added by redhat-upgrade-tool
Fix a crash if cleaning up without /var/lib/system-upgrade
Write GPG information to the yum repo files

Resolves: rhbz#1115532
New version 0.7.25