Run tests from test/ rather than build/test so that their assumptions
about paths hold true, fix a typo in the vm_listener_test line, and
mark prints_matcher_test failing on Safari.

R=kevmoo@google.com
TBR
See #4

Review URL: https://codereview.chromium.org//917353003

This fixes tests that don't require dart:io and marks those that do
dart:io as Skip.

R=kevmoo@google.com

Review URL: https://codereview.chromium.org//918853005

This also adds LiveTest.close, which releases resources associated with a
LiveTest.

R=kevmoo@google.com
See #2

Review URL: https://codereview.chromium.org//914963003

R=nweiz@google.com

Review URL: https://codereview.chromium.org//917503002

R=nweiz@google.com

Review URL: https://codereview.chromium.org//909323002

R=nweiz@google.com

Review URL: https://codereview.chromium.org//916523002

R=nweiz@google.com

Review URL: https://codereview.chromium.org//873473004

R=nweiz@google.com

Review URL: https://codereview.chromium.org//876343003