[RocksJava] GetIntProperty in RocksDB

Expose GetIntProperty methods to RocksJava. As the integer(64-Bit)
value is no integer in Java the method is aligned with the return
type which is long.
[RocksJava] Improved comments in RocksDB class

Improved comments in RocksDB getLongProperty methods,
to describe the behavior more detailed.
Merge pull request #397 from fyrz/RocksJava-GetIntProperty

[RocksJava] GetIntProperty in RocksDB
Options helper supports k, m, g, and t unit suffixes

Summary:
Add unit support in options helper so we can specify, e.g., 10m for
10 megabytes.

Test Plan: Updated options_test

Reviewers: sdong, igor, ljin

Reviewed By: ljin

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D28977