HBaseTimelineSchemaCreator has to allow user to configure pre-splits

Most of the TimelineService HBase tables is set with username splits which is based on lowercase alphabet (a,ad,an,b,ca,,,,). This won't help if the rowkey starts with either number or uppercase alphabet. We need to allow user to configure based upon their data. For example, say a user has configured the yarn.resourcemanager.cluster-id to be ATS or 123, then the splits can be configured as A,B,C,,, or 100,200,300,,,