Changes included in this version:

• allow conversions of CentOS and Oracle Linux 8
• fix "TypeError: execve()" py2.6-related error when calling external commands
• remove unused code related to using offline snapshot or RHEL repositories
• remove all Red Hat Network (RHN)-related code as RHN has been shut down
• set POSIX/C locale at the start of running the tool
• remove python-syspurpose dependency from spec - not available on OL 7 and 8
• not renaming the original system repofiles anymore
• replace the word blacklist with exclude/excluded
• clearing yum versionlock that could cause the conversion to fail
• printing rpm files that were modified during the conversion
• minor UX improvements and test infrastructure improvements