Summary:
Add a test to detect that when WAL gets truncated,
seq no's are checked to be contiguous.
This test is put in ColumnFamilyTest as it has the necessary
infrastructure/functions for flushing column families, which
we use to ensure 2 active WAL files
Test Plan:
This is a test, no feature has been added.
This test fails today and hence disabled
Reviewers: sdong
Reviewed By: sdong
Subscribers: lgalanis, dhruba, andrewkr, pritamdamania
Differential Revision: https://reviews.facebook.net/D59253
