Makefile: add -cover flag to `go test`
Makefile: add -cover flag to `go test`

coreos/ignition,dgonyeo/ignition,marineam/ignition,ajeddeloh/ignition,dgonyeo/ignition,marineam/ignition,dgonyeo/ignition,mischief/ignition,mischief/ignition,trnubo/ignition,trnubo/ignition,trnubo/ignition,jonboulle/ignition,mischief/ignition,AlexNPavel/ignition,jonboulle/ignition,AlexNPavel/ignition,coreos/ignition,ajeddeloh/ignition,coreos/ignition,crawford/ignition,ajeddeloh/ignition,jonboulle/ignition,higebu/ignition,higebu/ignition,marineam/ignition,crawford/ignition,AlexNPavel/ignition,higebu/ignition