feature request: make excluding tests

[andres-erbsen]

map solver tests take a while compared to rest of the repo

[samuelgruetter]

Here's how you can do that:

• Move all test files into a separate folder (eg a sibling of src, or src/test).
• In the Makefile, duplicate all rules and variable definitions containing all or ALL, replacing all/ALL by notest/NOTEST, and filter out the test files in the find command.
• In the toplevel Makefile of bedrock2, invoke $(MAKE) -C $(DEPS_DIR)/coqutil notest for the coqutil target, but do include a separate target called test_coqutil and make sure it runs when you do a toplevel make all.