Better error message when keys are not installed

[murphm8]

We require that users have keys added to their apt keys cache. When the keys aren't there an exception is thrown when we attempt to update our copy of the apt cache.

[cgibb]

When attempting to bundle without the OSRF keys, the error message is the following:

[26.391s] ERROR:colcon.colcon_bundle.verb:Could not fetch from repositories: W:Skipping acquire of configured file 'main/binary-i386/Packages' as repository 'http://packages.ros.org/ros2/ubuntu bionic InRelease' doesn't support architecture 'i386', W:GPG error: http://packages.osrfoundation.org/gazebo/ubuntu-stable bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 67170598AF249743, E:The repository 'http://packages.osrfoundation.org/gazebo/ubuntu-stable bionic InRelease' is not signed.
[26.392s] ERROR:colcon:colcon bundle: Failed to fetch from repositories. Did you set your keys correctly?