Change "Jar" job type to "MapReduce"

Changes the "Jar" job type to "MapReduce".  This maps more closely
to the underlying Oozie actions, and will help remove ambiguity when
Savanna supports Oozie "java" actions in the future.

Backward compatibility is supported as follows:
1) Any job created through the conductor with job type "Jar" will
have its job type automatically changed to "MapReduce"

2) Tests for job_type "Jar" have been changed to test for membership
in ["Jar", "MapReduce"]. This should support existing jobs in a
savanna database with type "Jar", even though all new jobs will be
"MapReduce"

These measures should allow this change to work with a UI which is
still using the "Jar" job type.

Closes-Bug: #1260829

Change-Id: I1ad59fa466b9a5d838c62bf366b642e453340bce
Merge "Change "Jar" job type to "MapReduce""