Add test that increment/append properly integrate with MVCC

We should test that increment/append properly integrate with MVCC.

HBASE-4583 fixes the issue for increment/append.

Here is a run through of the tests:

increment:
current cell value is 10. Issue concurrently a put of 50 and an increment by 1. Only acceptable values are 50 and 51 (not 11).

append:
current cell value is 'x'. Issue concurrently a put of 'y' and an append of 'x'. Only acceptable values after are 'y' and 'yx' (not 'xx').