Get rid of the AbtractWAL

Summary:
With the recent refactoring of the WAL we need to get rid of the
AbstractWAL and use the WALProvider.

This diff will just remove the use of AbstractWAL

Test Plan: hbase-consensus unit tests

Reviewers: reddragon, fantasist, eclark, tedyu

Differential Revision: https://reviews.facebook.net/D30681

Signed-off-by: Elliott Clark <eclark@apache.org>
Adding license headers to the hbase-consensus module

Summary:
The hbase-consensus classes were missing apache license headers.
I am adding them.

Total files : 234
Licensed files : 232

Remaining two files :
1. IllegalArgument.java (Auto generated)
2. rmap.json (data for test cases)

java -jar apache-rat-0.11.jar --exclude ./test/resources/org/apache/hadoop/hbase/consensus/rmap/rmap.json --dir ./

Test Plan: build and also run the rat tool

Reviewers: eclark, fantasist, reddragon

Differential Revision: https://reviews.facebook.net/D30687

Signed-off-by: Elliott Clark <eclark@apache.org>