HBASE-25278 Add CACHE_BLOCKS option to count shell command

Expose an argument on the `count` command which is passed to the
`setCacheBlocks` method on the Scan which the count command uses.

This is a quick and dirty approach to read all of the blocks for a table
into the block cache.

* Raise an error when the value isn't a boolean or the expected string

Closes #2650

Signed-off-by: Zach York <zyork@apache.org>
Signed-off-by: Peter Somogyi <psomogyi@apache.org>
2 files changed