test: Cleanup the test output

This makes the new, git-derived test suite report results in a manner
similar to the original notmuch test suite.

Notable changes include:

  * No more initial '*' on every line
  * Only colorize a single word
  * Don't print useless test numbers
  * Use "PASS" in place of "ok"
  * Begin sentences with a capital letter
  * Print test descriptions for each block
  * Separate each block of tests with a blank line
  * Don't summarize counts between each block