Make set*Param methods members to allow use in tests

Make set*Param methods members to allow use in tests

Moved set*Param methods to be members of EventuallyPersistentEngine to
simplify testing the logic therein. They were previously static methods
and were not callable directly from tests.

Change-Id: I263ed94149a0142de5838556eb34799ff02c9049
Reviewed-on: http://review.couchbase.org/76702
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>