Fix use of config.ssh.username and reset provisioning path permissions.

This commit contains two fixes:

- The Chef provisioner was incorrectly referencing config.ssh.username
  instead of machine.ssh_info[:username]. With the new change to default
  ssh configuration, if a user had not set config.ssh.username,
  provisioning would fail.

- The shell provisioner was not appropriately changing permissions to
  the upload path. If a different ssh user attempted to use a shell
  provisioner, provisioning would fail. The same case applied to
  the Chef provisioner -- while permissions were being reset, they
  were not done recursively.
Merge pull request #1576 from smdahlen/fix-ssh-username

Fix use of config.ssh.username and reset provisioning path permissions.