`mach bootstrap` will finish succesfully,
but then segfault inside glibc while exiting.
It seems to have to do with the MarkupSafe library used by Mako;
delaying the Mako import from the top level to inside functions where it
is used avoids the problem.
(It seems to interact with the call to pip to install the Salt
requirements in the virtualenv, as commenting that pip call out
separately will also fix the segfault.)

Also, use the Mako installed in the Python virtualenv while running
packaging commands (instead of the one from the bundled zip file),
and cleanup imports in the package_commands.py file.