…dates to arrays (#802)

- remove addons headers and replace with array and KV
- remove addons test and integrate with daos_test
- update READMEs
- remove multi dkey update/fetch API
- update the array README with new ARRAY format of a flat KV.
DKEY 0 will hold metadata. User data will start from DKEY 1.
- add implementation for daos_array_open_with_attr.
- use that instead of daos_array_create/open in DFS
- store the File chunk size in the entry attrs if it's not default
- add tests for array_open_by_addr

Signed-off-by: Mohamad Chaarawi <mohamad.chaarawi@intel.com>