Major Description
To enable grouping via Tez, users should not need to change the underlying InputFormat. A simple enable / disable option should be sufficient.
MRInputConfigurer does this.
Many of the methods in MRHelpers, however, require an InputFormat to be specified. The main objective of this JIRA is to get rid of this requirement in favor of a simple enableGrouping flag.
Marking this as a blocker for TEZ-1347, since it should simplify the set of APIs required. Also, making all the changes in TEZ-1347 would just lead to a very large patch.
