Move aws connection default/env handling to option parsing (#514)

aws_ssm connection - Move connection vars environment handling into options

SUMMARY
This fix moves a number of connection related variables to the options parsing step instead of inline. This has the added effect of documenting their existence and making overriding them more consistent with Ansible's UX.
Fixes #343
ISSUE TYPE

Bugfix Pull Request

COMPONENT NAME
aws_ssm
ADDITIONAL INFORMATION

There were a couple of other minor changes related to logging and silencing curl's progress info outside of the connection vars themselves. I'm happy to pull them out if desired and submit them as a separate PR.
I added fallback on hostnames lookup to match SSH's host handling since that's the defacto connection plugin. This incidentally fixes the way delegation is reported (it didn't show the -> delegated host bit in the logs).
Of note, the ec2.py module sets the instance_id and placement on instances it detects so I added it as first-class fallback for instance_id and region parameters respectively. The get_options parser doesn't handle nested variable lookups, so I had to modify the lookup slightly.

Reviewed-by: Jill R <None>
Reviewed-by: Guillaume GILL <None>
Reviewed-by: Mark Chappell <None>
(cherry picked from commit 94d1295)

changelogs/fragments/514-aws_ssm-env_vars.yml

@@ -0,0 +1,2 @@
+minor_changes:
+- aws_ssm - rework environment variable handling to use built in Ansible plugin support (https://github.com/ansible-collections/community.aws/pull/514).

plugins/connection/aws_ssm.py

@@ -24,16 +24,22 @@
     description: The STS access key to use when connecting via session-manager.
     vars:
     - name: ansible_aws_ssm_access_key_id
+    env:
+    - name: AWS_ACCESS_KEY_ID
     version_added: 1.3.0
   secret_access_key:
     description: The STS secret key to use when connecting via session-manager.
     vars:
     - name: ansible_aws_ssm_secret_access_key
+    env:
+    - name: AWS_SECRET_ACCESS_KEY
     version_added: 1.3.0
   session_token:
     description: The STS session token to use when connecting via session-manager.
     vars:
     - name: ansible_aws_ssm_session_token
+    env:
+    - name: AWS_SESSION_TOKEN
     version_added: 1.3.0
   instance_id:
     description: The EC2 instance ID.
@@ -43,6 +49,9 @@
     description: The region the EC2 instance is located.
     vars:
     - name: ansible_aws_ssm_region
+    env:
+    - name: AWS_REGION
+    - name: AWS_DEFAULT_REGION
     default: 'us-east-1'
   bucket_name:
     description: The name of the S3 bucket used for file transfers.
@@ -57,6 +66,8 @@
     description: Sets AWS profile to use.
     vars:
     - name: ansible_aws_ssm_profile
+    env:
+    - name: AWS_PROFILE
     version_added: 1.5.0
   reconnection_retries:
     description: Number of attempts to connect.
@@ -736,15 +747,6 @@ def _get_boto_client(self, service, region_name=None, profile_name=None, endpoin
         aws_secret_access_key = self.get_option('secret_access_key')
         aws_session_token = self.get_option('session_token')
 
-        if aws_access_key_id is None:
-            aws_access_key_id = os.environ.get("AWS_ACCESS_KEY_ID", None)
-        if aws_secret_access_key is None:
-            aws_secret_access_key = os.environ.get("AWS_SECRET_ACCESS_KEY", None)
-        if aws_session_token is None:
-            aws_session_token = os.environ.get("AWS_SESSION_TOKEN", None)
-        if not profile_name:
-            profile_name = os.environ.get("AWS_PROFILE", None)
-
         session_args = dict(
             aws_access_key_id=aws_access_key_id,
             aws_secret_access_key=aws_secret_access_key,