[tooling] check for incompatible environment for HBase 2.0 upgrade

from stack on HBASE-19158:

Server failure. HBase can still read HFiles written in the older version 2 format.

Need a script that user can run pre-upgrade.

Additional commentary from busbey

In addition to the config check stack mentions, such a tool could check

• other problematic configs, like those for master-hosts-regions
• inconsistent configs due to changed defaults (I think we should have some smell-tests around the change in default for hbase.security.authorization)
• (optionally) check for unreadable WALs
• (optionally) check for unreadable hfiles