contrib/install-autotest-server.sh: remove 2nd round of package installation

Nothing changes wrt to packages and repos between `install_packages` and
`update_packages`, so remove one of them.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
contrib/install-autotest-server.sh: install passwd package earlier

On Red Hat (like) systems, `passwd` is also needed at a very early
stage of the installation (before the complete package installation).

While we could assgin the password for the autotest user later (after
the full packages install), let's just make use of the same function
that installs git and call them "basic packages".

Signed-off-by: Cleber Rosa <crosa@redhat.com>