Fix cover_spec options for ct

[surik]

There is only cover option but rebar_prv_common_test.erl uses cover_spec

[ferd]

@talentdeficit ?

[talentdeficit]

i prefer to leave it as is so rebar3 ct --cover and rebar3 eunit --cover do the same thing but i guess we could always rename both

[ferd]

I'd rather stick with --cover personally and normalize on that.

[surik]

If we leave it as is how do we specify cover.spec files? ct:run_tests/1 doesn't have options cover_spec. This PR is not about CLI option --cover/-c it is about cover option for ct

I think we can do it little easier via transform_opts/2, I will rework it.

[surik]

Done

[talentdeficit]

+1, this looks fine to me