Catkin plugin doesn't support rosdep dependencies that resolve to pip

[Kyle Fazzari]

The Catkin plugin currently supports determining dependencies with rosdep and fetching them as stage packages. However, rosdep also supports resolving dependencies into pip. For example:

    $ rosdep resolve python-tzlocal-pip
    #pip
    tzlocal

This should be supported.

[Kyle Fazzari (kyrofa)]

The first step toward fixing this is to extract rosdep into its own area so it can be worked on without getting lost in the enormous catkin plugin. That's being done here: https://github.com/snapcore/snapcraft/pull/1392 .

[Kyle Fazzari (kyrofa)]

Support for actually parsing dependency types other than apt is here: https://github.com/snapcore/snapcraft/pull/1479 . Still not actually supporting pip, yet, but getting there. At least trying to use pip dependencies will be met with a nicer error, now.

[Kyle Fazzari (kyrofa)]

First step in extracting pip from the python plugin is to grab a set of helper functions required by pip: https://github.com/snapcore/snapcraft/pull/1540

[Kyle Fazzari (kyrofa)]

Next step is to extract the sitecustomize generation that will also be required by the Catkin plugin: https://github.com/snapcore/snapcraft/pull/1547

[Kyle Fazzari (kyrofa)]

The second to last step is the extraction of the pip wrapper itself: https://github.com/snapcore/snapcraft/pull/1549 .

[Kyle Fazzari (kyrofa)]

And finally, the last step is actually supporting pip dependencies in the Catkin plugin: https://github.com/snapcore/snapcraft/pull/1581