Adds the ability to clobber specific slaves

The clobber endpoint now supports passing in a specific slave, when a slave is specified
only lastclobber queries with that slave will have access to its clobbertime. Otherwise,
when no slave is specified, a NULL value is passed to the clobber_times table and any
slave will have access to its data. That is, NULL acts as a wildcard for slaves.
pep8 fix from validate.sh
Cleaning up formatting and comments.
Fixes a comment typo.
Gets rid of the nasty sleep in the tests.
Adds clarifying comment.
Merge pull request #6 from mrrrgn/clobber-logic

Clobber logic