pyctdev 0.6 is no longer testing installed conda packages

[ceball]

Ever since #14 (July 2019), generated conda packages are not being tested beyond the standard conda "import" test. So e.g. if a project requests that the generated packages should be installed and then the unit tested, the unit tests won't actually run for the installed conda packages. This doesn't affect unit tests on the development install, which do run. And it also doesn't affect python packages, which are still being tested as specified.

Does not affect 0.7 (unreleased), because it uses conda build in a different way.