PHOENIX-933 Local index support to Phoenix

Updated pull request after resolving conflicts and handling James review comments.
bq. why do we need this to be different for local indexes? Seems like we could run parallel scans over part of each region just like we do with other scans, no?
Index table rows have region start key as prefix so even if we split region key ranges into multiple and scan parallelly,only first scanner gives the results and remaining all the scanners just return nothing. So number of splits of local index region setting to 1.
if we want to start multiple scanners for local index into multiple parts then we need to split the scan ranges into multiple.