Define suites for subsets of unittests from each major area of the codebase

There is a way to run a subset of the unittests through resmoke.py, but it is not clear or intuitive how to do so. We should define YAML suite definitions for the different areas of the code base. Specifically:

• replication (build/**/repl/*)
• auth (build/**/auth/*)
• sharding (build/**/mongo/s/*)
• query (build/**/query/*)

Old description:
Right now when I want to run all the replication unit tests, I "scons build/unittests.txt", then I copy all the lines of unittests.txt that correspond to repl tests and paste that into the shell. Then I have to scroll up through the pages of output and visually parse the output looking for any indication that a test fails. This is incredibly involved and error prone. We need some way to run a group of unit tests and see clearly and succinctly if any of them failed.