Reorganize test files

- Separate tests into 'basic' and 'io' variants. The basic tests don't
  require a mock and don't need to be tested individually with each I/O
  plugin and can execute much faster without a mock or special
  environment variables

- Prepend each test with a 't_' rather than having 'foo-unit-test' where
  the 'unit-test' suffix is redundant

Change-Id: I2e7aff4b10b14a57b0dfff580b730f3d110aea88
Reviewed-on: http://review.couchbase.org/33941
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>