Move fakeDcpAddFailoverLog() from StreamTest to base class DCPTest
Move fakeDcpAddFailoverLog() from StreamTest to base class DCPTest

StreamTest is child class of DCPTest can implements fakeDcpAddFailoverLog.
But, fakeDcpAddFailoverLog can also be used by other child classes of
DCPTest like ConnectionTest. Hence it is better to have it in the
base class.

Change-Id: I94a7155811f1bc125dbc5073cd4704ee7826b359
Reviewed-on: http://review.couchbase.org/84648
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