[autotest] Force to use puppet version 3.8.4 for Vagrant.

vagrant_puppet_install Vagrant plugin failed to install puppet 3.4.2.
Use puppet 3.8.4 instead.

BUG=chromium:575021
TEST=Vagrant provision

Change-Id: Ibaabed4dccde05675f60981151b71642036c5d13
Reviewed-on: https://chromium-review.googlesource.com/321191
Reviewed-by: Mungyung Ryu <mkryu@google.com>
Tested-by: Mungyung Ryu <mkryu@google.com>
2 files changed