Import during solve

[carolynvs]

This epic covers all the tasks necessary before we can flip the switch on importing external config "on-the-fly" during solve.

• Import external configuration from dependencies during init #821 - Import external configuration from dependencies during init (see PR [WIP] dep: Enable importing other tools and add integration tests #1277)
• Import external configuration from dependencies during ensure #1358 - Import external configuration from dependencies during ensure
• Importers should not hard fail on errors #1315 - Importers should not hard fail on errors
• Importers need a more conservative mode for use during solve #1316 - Importers need a more conservative mode for use during solve

[allenpetersen]

As of v0.4.1 having prune set to unused-packages or non-go will remove manifest files from other tools, I've tested this with Godep.json files, I assume other tools have similar issues. Should prune be aware of the metadata files used by the Importers and prevent them from being deleted?

[carolynvs]

@allenpetersen I've split your question off into its own issue, since it's not related to this epic.

#1631

[carllhw]

Any progress ?