Truncate database between integration tests

  Instead of dropping and recreating each time.

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Only restart director in integration tests if configuration changed

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Switch to using go agent in shipit

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>