Old versions of git lack --force and --tags,
but the same effect can be had by specifying refspecs.

The test assumes that a directory with write permission removed isn't writable,
this isn't the case if the process running the tests has CAP_DAC_OVERRIDE
which is common when running as root.

test_track_invalid_submodule depends on being able to remove a submodule
by `git rm $submoduledir`, but old versions of git don't update .gitmodules
so BuildStream still thinks there's a submodule present.

For expediency the test is skipped rather than changed to manually remove
the entry from .gitmodules if git hasn't done it,
since in the common case git is new enough to do that itself.

test_git_describe expects --first-parent to find another tag,
but `bst track` will gracefully degrade if the option doesn't work
so a different history will be retained with old versions of git.

It's of marginal benefit to add additional cruft
to test for different output on old versions of git that won't persist forever.

Benjamin Schubert authored Dec 20, 2018 and richardmaw-codethink committed Jan 21, 2019

Centos is apparently different enough from fedora when running tests.

Fix CentOS

Closes #833

See merge request !1085

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