Cleanup scan related functions

Incorporated the comments from change id 331
Changed ExpHbaseInterface_JNI::fetchAllRows method to use the new scan methods
Removed the scan related methods that are no longer used

Triggered the cleanup of Java objects at the time of releaseHTableClient.
Increased the default maximum java heap size to 1024MB from 512MB.

Change-Id: I851bcfa266504f609fdbcba6f2a5e9e6dd2937d3
Merge "Cleanup scan related functions"