* Stop importing testing in the main binary

Stop importing "testing" into the main binary:

* test/helpers.go imported it; remote that and change function signature
* update all tests that use this
Signed-off-by: Miek Gieben <miek@miek.nl>

* Drop import testing from metrics plugin
Signed-off-by: Miek Gieben <miek@miek.nl>

* more fiddling
Signed-off-by: Miek Gieben <miek@miek.nl>