MB-7250: only sign at the project level, not at target also

Change-Id: I80e8f28b882dae910521d19b47a184045b0031ae
Reviewed-on: http://review.couchbase.org/28801
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>