Intermittent test failure (TraitError) in test_all_instantiable

CI runs fail occasionally with a test failure resembling that below. The bounds for the trait are the same each time, but I've seen different values appear in the `TraitError` (most recently, -1e-77), suggesting that that value may have come from something undefined.

```
======================================================================
FAIL: Test if all the TVTK classes can be instantiated
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/travis/build/enthought/mayavi/tvtk/tests/test_tvtk.py", line 934, in test_all_instantiable
raise AssertionError(message.format(''.join(errors)))
AssertionError: Not all classes could be instantiated:
Traceback (most recent call last):
File "/home/travis/build/enthought/mayavi/tvtk/tests/test_tvtk.py", line 929, in test_all_instantiable
tvtk_klass()
File "tvtk_classes/euclidean_cluster_extraction.py", line 74, in __init__
tvtk_base.TVTKBase.__init__(self, vtk.vtkEuclideanClusterExtraction, obj, update, **traits)
File "/home/travis/build/enthought/mayavi/tvtk/tvtk_base.py", line 367, in __init__
self.update_traits()
File "/home/travis/build/enthought/mayavi/tvtk/tvtk_base.py", line 520, in update_traits
setattr(self, name, val)
File "/home/travis/.edm/envs/edm/lib/python2.7/site-packages/traits/trait_handlers.py", line 236, in error
object, name, self.full_info(object, name, value), value
TraitError: The 'radius' trait of an EuclideanClusterExtraction instance must be 0.0 <= a floating point number <= 9.99999968029e+37, but a value of 1e+299 was specified.
```