CI: Add local feed for CI-built packages

CI: Add local feed for CI-built packages

To test each package, the CI-built target package (ipk) file is
installed, but currently the target package's dependencies are installed
from the standard opkg feeds.

There are cases when the CI-built target packages should be
installed/tested together:

* If a pull request contains several new packages that depend on each
  other, the test step will fail as the new dependencies cannot be found
  in the current packages feed.

* If a pull request upgrades a source package that builds several target
  packages that depend on each other, the test step may fail due to the
  version/ABI mismatch between a newer target package and the older
  dependencies installed from the packages feed.

This sets up a local feed for the CI-built packages so that dependencies
are also installed from the same set of packages.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>