Upgrade spymemcached to 2.11.0

Motivation
----------
Spymemcached 2.11.0 contains many changes that help with more stability
during authentication, reconneaction, and other scenarios. Also, more
methods are exposed for async mutating and typesafe status codes.

Modifications
-------------
Upgrade the dependency and adapt the test cases to fit with the new interface.

Result
------
Upgraded dependency.

Change-Id: I5543c028a2ee7c9bee0035d04f3fb576ee96bcf8
Reviewed-on: http://review.couchbase.org/35264
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>