[Makefile/checklicense] Scalability limit on files to check

[djaglowski]

This issue was noticed while attempting to bring the log-collection library into contrib. This change would bring in a substantial number of files, but as it turns out, the checklicense target fails due to an argument list that is too long. The failure message is very unhelpful as well.

make: execvp: /bin/sh: Argument list too long
make: *** Makefile.Common:79: checklicense] Error 127

Ultimately, the problem is that checklicense is being run with a list of files that is too long.

It turns out that when running checklicense in the root module, all files within the repo are listed and checked. However, golint also checks all files within each module's root directory. This isn't necessarily a problem in itself - it just means that most files are checked twice. However, it seems we cannot continue to increase the number of go files in the project without excluding at least some of this duplication, such that when checklicense runs for the root module, the list of files is limited.

#9762 demonstrates the problem in an isolated having the golint target running checklicense on an artificially long list of files.