WIP DB benchmarking tools

Change-Id: I3e12ee931aabc07b1d042fe373817b644e6aeaab
Add option to append to keys.

Change-Id: Ib8b670f1aea9b59791ae83d59dcda2406eaa18f7
Add "make exec" target.

Change-Id: I101d849e4812a1ac104877b9323a1f3956a02363
Add option to disable LevelDB compression.

Change-Id: Ied519e688dbcd9137e083a8f7fd80e20c57bd7a3
Foobar.
Add goleveldb and boltdb to dbbench suite.

Change-Id: Id2539e75beadf3318fa78e693eaefb67937b02a4