[cloud] EC2 dynamic inventory default filename is documented as ec2.ini - fixes #24396 (#24515)

* the default filename is ec2.ini

(to override that use the env var EC2_INI_PATH)

* allow fallback to ec2.ini

contrib/inventory/ec2.py

@@ -226,6 +226,7 @@ class Ec2Inventory(object):
 
         defaults = {
             'ec2': {
+                'ini_fallback': os.path.join(os.path.dirname(__file__), 'ec2.ini'),
                 'ini_path': os.path.join(os.path.dirname(__file__), '%s.ini' % scriptbasename)
             }
         }
@@ -236,6 +237,10 @@ class Ec2Inventory(object):
             config = configparser.SafeConfigParser()
         ec2_ini_path = os.environ.get('EC2_INI_PATH', defaults['ec2']['ini_path'])
         ec2_ini_path = os.path.expanduser(os.path.expandvars(ec2_ini_path))
+
+        if not os.path.isfile(ec2_ini_path):
+            ec2_ini_path = os.path.expanduser(defaults['ec2']['ini_fallback'])
+
         config.read(ec2_ini_path)
 
         # is eucalyptus?