builder/amazon: Fix issue with sharing AMIs with ami_users

clean up character encodings

website: Fix DigitalOcean section of getting started docs.

This updates the example for adding DigitalOcean
as a provider in the beginning tutorial. It looks
like it hadn't been updated in some time, and
was using old settings. I've updated it and
confirmed it works.

helper/communicator: support disabling SSH agent

builder/amazon-chroot: add mount_options configuration option

builder/qemu: default acceleration to tcg on Windows [GH-2284]

builder/amazon-chroot: various fixing and debugging of chroot builder

fix file download provisioner

allow import qemu builded artifacts

Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>

when file used with download direction we don't need
to check source on builder because it on machine.
Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>

These are needed for chroot builder to work