Create empty coverage profile from problem code to calculate coverage
correctly. For some wierd reasons it will also account for not tested packages.
This change prevents students from adding new code and testing it,
instead of getting good coverage for initial codebase :)
Currently, packages in coverme without tests created by student
are not checked for coverage, because no there are no test targets
for them at all!
The issue can be fixed by simply creating empty !change files,
but we are engineers, aren't we? :)
Bonus point: it prevents new packages from giving false coverage credit.
For example, mock file generated by gomock will have lots of covered code
almost instantly. However, the task can be hacked by adding new code to
existing packages.
This seems to be fair, especially since coverage target is
defined problem-wise. Practical reason: coverme/app can not
be covered sufficiently without testing Start/initRoutes/run;
out of these, only initRoutes can be tested, and testing it
separately is a wierd solution.
