Address pytest warnings (#3629)

* Address `boto` deprecation warnings

This commit eliminates the following warning:

../boto/ec2/connection.py:582:
  PendingDeprecationWarning: The current get_all_instances implementation will be replaced with get_all_reservations.

`boto` isn't likely to ever make good on this warning, but doing the replacement will
declutter the `moto` test output.

* Remove `invoke_lambda` tracebacks from unit test logging

If an exception is encountered, the details are returned in the response payload.
Printing the traceback was just adding noise to the pytest output.

* Use known AMIs in unit tests

This commit eliminates the following warning in the pytest output:

`PendingDeprecationWarning: Could not find AMI with image-id:ami-123456, in the near future this will cause an error.`

Known, pre-loaded AMI image ids are used instead of random ids that don't actually
exist in the moto backend.  The integrity of the tests is unaffected by this change.

A test has been added to provide explicit coverage of the PendingDeprecationWarning
raised when an invalid AMI image id is passed to moto.

tests/test_ssm/test_ssm_cloudformation.py

@@ -3,6 +3,7 @@ import json
 
 
 from moto import mock_ssm, mock_cloudformation
+from tests import EXAMPLE_AMI_ID
 
 
 @mock_ssm
@@ -15,7 +16,7 @@ def test_get_command_invocations_from_stack():
             "EC2Instance1": {
                 "Type": "AWS::EC2::Instance",
                 "Properties": {
-                    "ImageId": "ami-test-image-id",
+                    "ImageId": EXAMPLE_AMI_ID,
                     "KeyName": "test",
                     "InstanceType": "t2.micro",
                     "Tags": [