Add WithMeta unit tests

Add WithMeta unit tests

Create a test-suite using the SingleThreaded store test to drive
the with_meta commands.

The test-suite so far tries to exercise many of the error and success
paths.

The intent is to give a starting point for more comprehensive and easy
to understand *with_meta tests as opposed to the extension of the
testapp tests.

Change-Id: I4bdfec9879de3a9671fed820f9b5aab0ac7d2c71
Reviewed-on: http://review.couchbase.org/76381
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>