cylc run: support "now" as a start tag.
In the test-battery, poll before wait.

This gets the result from each test as it comes in without blocking on
the long-running suites.
test-battery: don't print run dir location.
Two test suites inadvertantly using 'at' scheduler

and would therefore fail if atd was not running.
test-battery: validation failure should be a test failure.
Checked all test suite tasks run as fast as possible.
A simple wait-and-retry loop for the name registration DB.

This only matters if you attempt to register several suites at the same
time, which one test suite now does.
test-battery: only validate the first time through.
Merge branch 'master' into cylc-run.now
Restore sequential sub-suites in tests/events/suite.
Merge pull request #459 from matthewrmshin/cylc-run.now

cylc run: support "now" as a start tag.
Documented 'cylc run now'.
Merge pull request #460 from hjoliver/some-test-battery-improvements

Some test battery improvements