zerovm-cli/build.sh: add missing python3 install

In order to run tox's python3 environment, we obviously need python3
installed.
buildenv.sh: remove quotation from scp call

The lxc_scp function wraps scp, and the args ($*) we being wrapped in
quotes, which was causing a command syntax error.
zerovm-cli/package.sh: install missing deb pkgs

devscripts and debhelper were missing; we need these to roll packages
(dch, debuild, etc.).
toolchain: overwrite ~/.bashrc instead of prepending

We would like to set ZRT_ROOT when the generic package.sh script is
run. The build commands are executed SSH, which means that we have a
non-login non-interactive shell. Bash (the shell on the build machine)
would then normally not execute ~/.bashrc or ~/.bash_profile. However,
Bash has code to detect when it's started by sshd and will then
execute ~/.bashrc despite the session being non-interactive.

Ubuntu ships with an elaborate default .bashrc file, which among other
things exit early if it sees that $PS1 is empty. An empty $PS1 is a
sign that the session is non-interactive. This defeats the purpose of
Bash executing the ~/.bashrc file!

Since we don't want or need the Ubuntu defaults, so we just overwrite
the ~/.bashrc file. This simplifies the whole thing and removes
assumptions about the Ubuntu default ~/.bashrc file.
Merge pull request #19 from mgeisler/master

toolchain: overwrite ~/.bashrc instead of prepending
packager.py: fix tar archive file collection

Previously, we were creating tarballs for packaging by including * and
excluding debian/. This works for many cases, but causes errors if a
project repo contains files beginning with ".". `debuild` will fail in
this case, resulting in a "local changes detected" error (because there
is a `.whatever` file in the local clone which is not present in the
tarball).

This change fixes that by add more explicit file inclusion glob patterns
and --exclude directives.
Merge pull request #20 from larsbutler/fix-tar-archiving

packager.py: fix tar archive file collection