cache the pip tarball

there is no need to download the pip tarball over and over again
on rerun. Use the cached value.

Change-Id: Ibcc1807ba2aca062f69839212f05ac9394db9448
Merge "cache the pip tarball"
Update compute driver name for Ironic

Commit 08448e3a mistakenly updated the location of the Ironic compute
driver to be loaded from within the Nova tree.  However, no such module
exists as the compute and scheduler drivers both live in the Ironic tree.
This reverts that and adds a note explaining the setting.

Change-Id: I7f32f77bd7e5fd1f6b41014ac71bbf6e1a7d84cf
don't use pip -e install for libraries

libraries in openstack shouldn't be installed editable, as it
causes all manner of issues (especially complicated by the use
of namespace packages). Install these globally as part of the
devstack installation process.

Change-Id: I11acb169e74069be0618e57496ff342f9e788493
Merge "Fix Neutron plugin XTRACE handling"
Merge "don't use pip -e install for libraries"