Calculate coverage for libcalico-go as a whole
Calculate coverage for libcalico-go as a whole

More specifically, and borrowing some magic from Felix,
- in each test suite, record coverage for all libcalico-go packages, not
  just those in the same directory as the test suite
- merge coverage profiles from each test suite into a single
  'combined.coverprofile'.

insequent/libcalico-go,projectcalico/libcalico-go,insequent/libcalico-go,projectcalico/libcalico-go