Fix configuration dump with inline encrypted variables

If inline Ansible vault encryption is used to define an encrypted
variable in kayobe-config, running 'kayobe configuration dump -l <host>'
fails with the following:

  Failed to decode config dump YAML file /tmp/tmp_fg1bv_j/localhost.yml:
  ConstructorError(None, None, "could not determine a constructor for
  the tag '!vault'", <yaml.error.Mark object at 0x7f1e5c7404c0>)

This change fixes the error by using the Ansible YAML loader which
supports the vault tag. Any vault encrypted variables are sanitised in
the dump output. Note that variables in vault encrypted files are not
sanitised.

Change-Id: I4830500d3c927b0689b6f0bca32c28137916420b
Closes-Bug: #2031390