log level.

- support functions for logging at different levels.
- changed the log.* calls to level based logging for `adminport`.

Change-Id: I69faa13cb54c14f27334e723082241ba22760c06
Reviewed-on: http://review.couchbase.org/38170
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>