Maintain WAL metadata in operator state.
Use window-ids as log sequence numbers.
Merge branch 'hds' of github.com:DataTorrent/Malhar into hds

Conflicts:
	contrib/src/main/java/com/datatorrent/contrib/hds/HDSBucketManager.java
	contrib/src/test/java/com/datatorrent/contrib/hds/WALTest.java
Merge pull request #1009 from sashadt/hds

Hds
Merge branch 'hds' of https://github.com/tushargosavi/Malhar into tushargosavi-hds

Conflicts:
	contrib/src/main/java/com/datatorrent/contrib/hds/HDSBucketManager.java
	contrib/src/main/java/com/datatorrent/contrib/hds/HDSFileAccess.java
Fix merge conflict.
Merge pull request #1010 from tweise/hds

Hds
Move WAL interfaces
Merge pull request #1014 from tweise/hds

Move WAL interfaces
Add test for get
Merge pull request #1015 from tweise/hds

Add test for get
Relocate file access mock to test package.
Merge pull request #1016 from tweise/hds

Relocate file access mock to test package.
Add default key comparator.
HDSFileAccess unit test.
For now, for TFile and HFile implementation
Changes to make test pass
test utilities
Merge pull request #1020 from tweise/hds

Add default key comparator.
Merge pull request #1021 from siyuanh/hds1

Fix bugs and add unit test for TFile/HFile FileAccess impl
Adding support for environment variables during performance testing