Bug squash

Improvements over 3.9 which include

spread tests: set en_US.UTF-8 locale to plainbox run

Plainbox tests require a unicode locale to be set.

travis: use stable channel for shellcheck snap

Fixes failure with:

shellcheck: src/ShellCheck/Analytics.hs:1825:10-27:
No instance nor default method for class operation mappend

colcon plugin: support ROS 2 Eloquent

Add support for the newest ROS 2 release, Eloquent Elusor. For more information about the release, see ros2/ros2#734.

catkin plugin: remove rospack workaround now that rosdep -i works (#2833)

Reverts a change made in #2585 now that rosdep has grown the ability to ignore source packages on its own.

plugs/slots: use default interface if none is specified (#2840)

Avoid a Traceback for when a plug has no subelement.

meta: convert Application's adapter from string to enum (#2856)

Introduce enum ApplicationAdapter to use instead of strings. Remove the unused Adapter equivalent found in project loader.

meta: do not set snapcraft-runner when adapter is "none" (#2853)

When adapter == "none", snapcraft should not modify the command or command-chain. However snapcraft presently ignores the adapter setting when it comes time to set the command-chain.

Instead, honor when adapter is "none". With these changes, given a snapcraft yaml:

<snipped>
apps:
  adapter-none:
    command: test-cmd
    adapter: none
  adapter-full:
    command: test-cmd
    adapter: full
  adapter-legacy:
    command: test-cmd
    adapter: legacy
  wrapped-default:
    command: test-cmd --test "@"
<snipped>

Will now yield:

apps:
  adapter-full:
    command: test-cmd
    command-chain:
    - snap/command-chain/snapcraft-runner
  adapter-legacy:
    command: test-cmd
    command-chain:
    - snap/command-chain/snapcraft-runner
  adapter-none:
    command: test-cmd
  wrapped-default:
    command: command-wrapped-default.wrapper
    command-chain:
    - snap/command-chain/snapcraft-runner