Cannot merge grains in salt-cloud deploy

Description of Issue/Question

If grains settings are placed in /etc/salt/cloud, they are overwritten by grains settings in any provider config. This is unfortunate, as it prevents placing global grains in a single location.

Setup

/etc/salt/cloud:

# Global server grains.
grains:
  server:
    env: production
    type: cloud
    group: video

/etc/salt/cloud.providers.d/linode.conf:

linode:
  driver: linode
  apikey: foo
  password: bar
  grains:
    server:
      provider: linode

/etc/salt/cloud.profiles.d/linode.conf:

linode-test:
  provider: linode
  image: Debian 8
  location: Dallas, TX, USA
  size: Linode 1024

/etc/salt/grains of created minion:

server:
  provider: linode

Steps to Reproduce Issue

• Create the above /etc/salt/cloud, /etc/salt/cloud.providers.d/linode.conf, and /etc/salt/cloud.profiles.d/linode.conf files on a master
• Run salt-cloud -p linode-test test
• Observe that /etc/salt/grains on the created test minion does not contain the grains as provided in /etc/salt/cloud.

Versions Report

Salt Version:
Salt: 2017.7.2

Dependency Versions:
cffi: 0.8.6
cherrypy: Not Installed
dateutil: 2.2
docker-py: Not Installed
gitdb: Not Installed
gitpython: Not Installed
ioflo: Not Installed
Jinja2: 2.9.4
libgit2: Not Installed
libnacl: Not Installed
M2Crypto: Not Installed
Mako: Not Installed
msgpack-pure: Not Installed
msgpack-python: 0.4.2
mysql-python: 1.2.3
pycparser: 2.10
pycrypto: 2.6.1
pycryptodome: Not Installed
pygit2: Not Installed
Python: 2.7.9 (default, Jun 29 2016, 13:08:31)
python-gnupg: Not Installed
PyYAML: 3.11
PyZMQ: 14.4.0
RAET: Not Installed
smmap: Not Installed
timelib: Not Installed
Tornado: 4.2.1
ZMQ: 4.0.5

System Versions:
dist: debian 8.10
locale: UTF-8
machine: x86_64
release: 3.16.0-4-amd64
system: Linux
version: debian 8.10

Start with the salt-cloud deployment path invoked by salt-cloud -p linode-test test, then trace how /etc/salt/cloud and provider configuration files are loaded and combined. Done means the created minion retains both the global server grains and the provider-specific provider: linode grain.