ci: Include coverage data of the 'client' package when running the main tests
ci: Include coverage data of the 'client' package when running the main tests

The main tests make heavy usage of the client package. The -coverpkg
option allows to include more package than only the package currently
tested in the coverage data.

Including the client package shows we indeed cover quite a bit of it
(80%) from the main tests.

Signed-off-by: Damien Lespiau <64bd3cb94f359c1a3ce68dae5e26b40578526277@intel.com>

clearcontainers/proxy,clearcontainers/proxy