test: rename test exec

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
zlog: add append log operation

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
zlog: fix return value check

Negative error codes are always errors, but zlog level errors may be
encoded as postive values.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
zlog: add fill log operation

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
zlog: add read log operation

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
Merge pull request #2 from cruzdb/wip-zlog-ops

add append, read, fill log operations