Fix default path for SLA files
Fix default path for SLA files

When invoked from the unit tests we don't specify a root path,
which caused all tests to be run without any SLA configured
(causing the slow op threshold to be set to 0ns ;-) )

Change-Id: I62425e262108f7265f2ab2e8afed89dab102b12d
Reviewed-on: http://review.couchbase.org/92299
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