The Docker API may either return an empty "OnBuild" or omit the
field altogether if it's not set.
Adjust the tests to make either satisfy the test.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Fix & enable SSH integration test suite.
This also adds a new test for connecting to unknown hosts when
using the Python SSH implementation (Paramiko). See #2932 for
more info.
Because of the above, some of the config/static key files have been
moved around and adjusted.
Signed-off-by: Milas Bowman <milas.bowman@docker.com>