build: do not process source files when build and testing

Signed-off-by: Leonardo Grasso <me@leonardograsso.com>

update(pkg/api/**/mocks): API mocks (for testing) should be checked in

Fixes falcosecurity#46

Co-authored-by: Lorenzo Fontana <lo@linux.com>
Signed-off-by: Leonardo Di Donato <leodidonato@gmail.com>