Try to run more of the testsuites on top of ep engine
Try to run more of the testsuites on top of ep engine

Up until now we've run the end to end tests (over the wire) purely
on default_engine. This have had the unfortunate side effect that
we haven't discovered the cases where ep-engine and default-engine
differ in return value for certain operations (we've had cases where
default_engine returns locked, and ep-engine returns tmpfail etc).

This patch adds an ENGINE parameter to specify the name of an engine
to test in _addition_ to default_engine. This patch should be modified
at some point by renaming ENGINE to ENGINES and contain a list of
all of the engines we want to run the test suite on top of.

Change-Id: Icd2a7b6fe184439d3fda17a227bc56d99bcb96db
Reviewed-on: http://review.couchbase.org/83124
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine