Pipeline includes exception type when reporting an error thrown by a
Callable
Fix NullPointerException that could be thrown while handling an error
during the scan
Updated ConstantVelocityScanLineTest to reflect change to
AbstractContinousScanLine

The change was that setOperatingContinuously() and
setHardwareTriggering() are now called earlier during the scan than used
to be.
In TrajectoryScanLineTest replaced DeferredAndTrajectoryScannableGroup
with a mock ContinuouslyScannableViaController

Changed required as a change to DeferredAndTrajectoryScannableGroup
broke this test. Solution was to decouple the two using the mock.