Salt orchestrate fails when no cloud providers are configured

Description of Issue

What it says on the tin

Setup

docker run --rm -it waynew/salt-sprints:3000
mkdir -p /srv/salt/orch
cat << EOF >/srv/salt/orch/fnord.sls
salt-cloud-create:
  salt.parallel_runners:
  - runners:
      instance-cloud-create-runner-1:
      - name: cloud.create
      - kwarg:
          instances:
          - instance.cloud
          provider: ec2-provider
          availability_zone: us-west-2
          image: ami-04cf43aca3e6f3de3
          size: t3.small
          rename_on_destroy: true
          ssh_username: centos
EOF

Steps to Reproduce Issue

salt-call --local state.orchestrate orch.fnord

This blows up with:

local:
    ----------
    data:
        ----------
        kevin:
            ----------
            salt_|-salt-cloud-create_|-salt-cloud-create_|-parallel_runners:
                ----------
                __id__:
                    salt-cloud-create
                __run_num__:
                    0
                __sls__:
                    orch.fnord
                changes:
                    ----------
                comment:
                    An exception occurred in this state: Traceback (most recent call last):
                      File "/usr/lib/python3.6/site-packages/salt/state.py", line 1981, in call
                        **cdata['kwargs'])
                      File "/usr/lib/python3.6/site-packages/salt/loader.py", line 1977, in wrapper
                        return f(*args, **kwargs)
                      File "/usr/lib/python3.6/site-packages/salt/states/saltmod.py", line 881, in parallel_runners
                        six.itervalues(outputs)]
                      File "/usr/lib/python3.6/site-packages/salt/states/saltmod.py", line 880, in <listcomp>
                        [out.get('outputter', '') == 'highstate' and 'data' in out for out in
                    AttributeError: 'bool' object has no attribute 'get'

That's because https://github.com/saltstack/salt/blob/v3000/salt/cloud/__init__.py#L403 says return False, which is not the kind of output that's expected - that code in saltmod requires out to be a dictionary.

Looking at the way saltmod is structured, probably the correct thing to do is account for False in the listcomp, and then again in https://github.com/saltstack/salt/blob/v3000/salt/states/saltmod.py#L904-L942

Though, it should also probably warn like suggested in this issue

Versions Report

salt-call --versions-report
Salt Version:
           Salt: 3000

Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: Not Installed
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
         Jinja2: 2.11.1
        libgit2: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.6.2
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.6.8 (default, Aug  7 2019, 17:28:10)
   python-gnupg: Not Installed
         PyYAML: 5.3
          PyZMQ: 19.0.0
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.3.2

System Versions:
           dist: centos 7.6.1810 Core
         locale: ANSI_X3.4-1968
        machine: x86_64
        release: 4.19.76-linuxkit
         system: Linux
        version: CentOS Linux 7.6.1810 Core

Reproduce the failure with salt-call --local state.orchestrate orch.fnord, then inspect the False return in salt/cloud/__init__.py and its handling in salt/states/saltmod.py. Trace parallel_runners through the referenced list comprehension and following lines; done means orchestration handles the no-provider result without an AttributeError and preserves the intended warning behavior.