libcephfs: expose stripe unit granularity

Assists clients in choosing layout parameters.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
java: add support for get_stripe_unit_granularity

Signed-off-by: Joe Buck <jbbuck@gmail.com>
Reviewed-by: Noah Watkins <noahwatkins@gmail.com>
java: fix whitespace

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
java: update javadoc comments

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
java: add stripe unit granularity tests

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>