Enabling default build; adding memcached.
Updating memcache tests for libmemcached >=2.1.0.

Since version 2.1.0 of libmemcached `getServerList()` doesn't include the `weight` value anymore.
Merge pull request #1037 from davidpersson/fix-memcache-tests

Enable Memcache in CI and adapt tests to newest version of libmemcached