Avoid monkey patching shlex globally (fixes test broken by 49c2bbb)
Build dxpy source distribution and use pip to install from it

This is needed because when using dxpy's "setup.py install", the
resulting installation injects a setuptools path into sys.path before
our own path, causing us to rely on an external pkg_resources file
from setuptools, and if that is too far out of date, it's unable to
resolve newer-format dependencies (ones that use "dist-info"
directories).

In particular, this should resolve the
"pkg_resources.DistributionNotFound: requests==2.3.0" message on
CentOS.
Re-add pip/setuptools installation
Complete rename of target
Re-add test deps install
Update copying of libs to follow new installation method
Fix directory intialization