use_artifact_config added as an optional default arg, allowing
for loading of given elements artifact remote config.

Provide bst shell --use-buildtree the ability to attempt to
acquire missing buildtrees, given respective option, user
pull-buildtree context and remote availability.

_frontend/cli.py: Refactor logic for determining --use-buildtree
option with given opportunity to attempt pulling a non-local
buildtree. Element loaded with artifact_config to allow remote
querying.

_stream.py: With given user option and element state, construct
PullQueue to fetch remote buildtree. Continue or Error without
buildtree if cannot be attained.

tests/integration/build-tree.py: Update to support new usecases

Download buildtrees on demand for bst shell --use-buildtree

Closes #829

See merge request !1050

Abderrahim Kitouni authored Jan 27, 2019 and Abderrahim Kitouni committed Jan 28, 2019

the code for initializing remotes added the project specific remote
caches to the global list instead of making a copy.

Abderrahim Kitouni authored Jan 28, 2019 and Abderrahim Kitouni committed Jan 28, 2019

This makes a junction use the artifact cache of the parent project
before the ones defined for the junction

Fixes #401