nios_a_record fails when using environment variables for provider data

[murrahjm]

Given the following sample code:

infoblox.nios.nios_a_record:
  name: testrecord.domain.com
  view: default
  ipv4addr: 10.10.10.10

with the following environment variables set:

INFOBLOX_HOST
INFOBLOX_USERNAME
INFOBLOX_PASSWORD

the task fails with this error:

"ansible.module_utils.api.get_connector() argument after ** must be a mapping, not NoneType"

I think it's referencing this line:

infoblox-ansible/plugins/module_utils/api.py

Line 244 in 1c94771

self.connector = get_connector(**provider)

[murrahjm]

Just playing around I was able to fix this by changing this line:

infoblox-ansible/plugins/module_utils/api.py

Line 244 in 1c94771

self.connector = get_connector(**provider)

to this:

self.connector = get_connector(**(provider or {}))

basically allowing an empty value to get passed, which will then be populated with the NIOS_PROVIDER_SPEC (unless provider is explicitly passed, in which case it will use that)

My python isn't great so I have no idea if this is the correct way to fix it, but I tested it in my environment and it seemed to function at least with the nios_a_record module. Happy to do a pull request is this is valid.