[salt-cloud]Defining `script_args: -j json_object` at provider level does not work with openstack driver

Description of Issue/Question

Under salt-cloud 2019.2, using script_args at provider level to pass options -j json_object to bootstrap-salt fails because openstacksdk tries to apply a python formatting to all config options and curly braces in json object fails python formatting.
The culprit line of openstacksdk code is here

Escaping curly-braces does not work.
Doubling them to escape python-formatting let you instanciate VM but this fails later on when executing bootstrap-salt because this is not a valid json object anymore.

Workaround is to move the script: and script_args configuration at profile level but, hey, who wants to duplicate configuration in each profile if they are the same everywhere?

Setup

Note: I don't use /etc/openstack/cloud.yml but rather define all provider onfiguration in /etc/salt/cloud.provider.d/<provider>.conf
Note2: If relevant, I use OVH public cloud, based on openstack

Using salt-cloud 2019.2 on Debian 9.

/etc/salt/cloud.providers.d/ovh-gra3.conf:

ovh-gra3:
  driver: openstack
  region_name: GRA3
  profile: ovh
  auth:
    username: REDACTED
    password: 'REDACTED'
    project_id: REDACTED
    project_name: 'REDATED'

  ssh_interface: private_ips
  ssh_key_name: my_ssh_key
  ssh_key_file: /path/to/keyfile

  minion:
    master: salt-master

  script: bootstrap-salt
  script_args: |
    -j '{"master": "salt-master"}' stable 2019.2
	
  security_groups:
    - no-input

  nics:
    - net-id: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx	
    - net-id: yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy

/etc/salt/cloud.providers.d/ovh-gra3.conf:

ovh-gra3_s1-2_deb9base:
  provider: ovh-gra3
  size: s1-2
  image: 'Debian 9'
  ssh_username: 'debian'

Steps to Reproduce Issue

(Include debug logs if possible and relevant.)

# cat my-cloud.map 
ovh-gra3_s1-2_deb9base:
  - test-saltcloud.company.tld

# salt-cloud -m my-cloud.map 
The following virtual machines are set to be created:
  test-saltcloud.company.tld

Proceed? [N/y] y
... proceeding
[ERROR   ] Failed to create VM test-saltcloud.company.tld. Configuration value u'"master"' needs to be set
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/salt/cloud/__init__.py", line 1288, in create
    output = self.clouds[func](vm_)
  File "/usr/lib/python2.7/dist-packages/salt/cloud/clouds/openstack.py", line 682, in create
    conn = get_conn()
  File "/usr/lib/python2.7/dist-packages/salt/cloud/clouds/openstack.py", line 320, in get_conn
    conn = shade.openstackcloud.OpenStackCloud(cloud_config=None, **vm_)
  File "/usr/local/lib/python2.7/dist-packages/shade/openstackcloud.py", line 146, in __init__
    cloud_config = config.get_one_cloud(**kwargs)
  File "/usr/local/lib/python2.7/dist-packages/openstack/config/loader.py", line 1066, in get_one
    config[key] = value.format(**config)
KeyError: u'"master"'
test-saltcloud.company.tld:
    ----------

Versions Report

# salt-cloud --versions-report
Salt Version:
            Salt: 2019.2.0
 
Dependency Versions:
 Apache Libcloud: 1.5.0
            cffi: 1.12.3
        cherrypy: Not Installed
        dateutil: 2.5.3
       docker-py: Not Installed
           gitdb: Not Installed
       gitpython: Not Installed
           ioflo: Not Installed
          Jinja2: 2.9.4
         libgit2: 0.24.5
         libnacl: Not Installed
        M2Crypto: 0.24.0
            Mako: Not Installed
    msgpack-pure: Not Installed
  msgpack-python: 0.4.8
    mysql-python: Not Installed
       pycparser: 2.19
        pycrypto: 2.6.1
    pycryptodome: Not Installed
          pygit2: 0.24.2
          Python: 2.7.13 (default, Sep 26 2018, 18:42:22)
    python-gnupg: Not Installed
          PyYAML: 3.12
           PyZMQ: 16.0.2
            RAET: Not Installed
           smmap: Not Installed
         timelib: Not Installed
         Tornado: 4.4.3
             ZMQ: 4.2.1
 
System Versions:
            dist: debian 9.9 
          locale: UTF-8
         machine: x86_64
         release: 4.9.0-8-amd64
          system: Linux
         version: debian 9.9 

Reproduce the failure with the provider and profile configuration shown, then trace salt/cloud/clouds/openstack.py, especially get_conn, into openstack/config/loader.py at the cited line. Determine where provider-level script_args are passed through formatting, and consider the existing profile-level workaround when defining the expected behavior; the issue is resolved when the shown configuration can create a VM and execute bootstrap-salt with the JSON argument intact.