remove executor's dependency on warden

this only works if they're colocated, which is a requirement we're trying to
move away from

Signed-off-by: Brannon Jones <brannon.jones@tier3.com>
add executor.backend_plugin property

this can be used to switch the executor to windows mode

this is an interim solution so long as we need backend plugins in the
executor; this is currently only required because the warden api doesn't speak
environment variables, so the executor needs logic itself

Signed-off-by: Brannon Jones <brannon.jones@tier3.com>
namespace warden client properties under executor

Signed-off-by: Brannon Jones <brannon.jones@tier3.com>