ACCUMULO-2988 Add check for older versions

We need to detect
That the version is one four
To do an upgrade
ACCUMULO-1010 Support upgrades from 1.4 to 1.5

Description: Add steps necessary to move a zk from 1.4 state to 1.5.
  This leaves it in a good state to be picked up by the rest of the
  1.6 upgrade path.
Author: kturner
Ref: ACCUMULO-2988

Cherry picking caused a huge mess and it was simpler to manually select
the parts of the upgrade code that we needed based on the 1.5.1 tag.

Gathered from commits 317c669, aa6b4309, and 8811859.
ACCUMULO-1264 move !METADATA file delete markers

Description: Move the !METADATA file delete markers out of the
  !METADATA table and to the root table on upgrade.
Author: Eric Newton
Ref: ACCUMULO-2988

Modified from commit 5416eef
ACCUMULO-2988 Upgrade from 1.4 -> 1.6.

* add a README section
* add log messages around upgrade actions
* change 1.4 -> 1.5 upgrade action around compaction cancellation to use 1.6 method of enumerating table ids.

Author: Sean Busbey <busbey@cloudera.com>
ACCUMULO-2988 Clean up of upgrade related constants and checks.