JSCBC-104 adding bucket flush support

* adding flush method to Connection including tests
* adding access to the bucket name via _bucket in Connection
* adding support for empty response body on HTTP requests
* exporting the POST Methond from the constants.cc

Change-Id: I65edc11d308e9d98ac7b72cef4b8e4bfccf7351a
Reviewed-on: http://review.couchbase.org/36132
Tested-by: Philipp Fehre <philipp@couchbase.com>
Reviewed-by: Brett Lawson <brett19@gmail.com>
Clarify memdbench usage

- Remove older output from older version in comments
- Replace with more recent output
- Mention that tests with eden's client requires a memcached bucket with
  a dedicated port

Change-Id: I1c753ed1744bd66ad7755d9817e932ad3dd8013a
Reviewed-on: http://review.couchbase.org/37182
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>