[cloud][inventory] Let ec2.py be renamed and search for a matching .ini file (#21567)

With this proposed PR, we want to make the use of many ec2 dynamic inventory files more flexible.
We are using multiple AWS accounts. We want to use different ini file (one for every account) and only one ec2.py.

contrib/inventory/ec2.py

@@ -220,12 +220,22 @@ class Ec2Inventory(object):
 
     def read_settings(self):
         ''' Reads the settings from the ec2.ini file '''
+
+        scriptbasename = __file__
+        scriptbasename = os.path.basename(scriptbasename)
+        scriptbasename = scriptbasename.replace('.py', '')
+
+        defaults = {'ec2': {
+            'ini_path': os.path.join(os.path.dirname(__file__), '%s.ini' % scriptbasename)
+            }
+        }
+
         if six.PY3:
             config = configparser.ConfigParser()
         else:
             config = configparser.SafeConfigParser()
-        ec2_default_ini_path = os.path.join(os.path.dirname(os.path.realpath(__file__)), 'ec2.ini')
+        ec2_ini_path = os.environ.get('EC2_INI_PATH', defaults['ec2']['ini_path'])
-        ec2_ini_path = os.path.expanduser(os.path.expandvars(os.environ.get('EC2_INI_PATH', ec2_default_ini_path)))
+        ec2_ini_path = os.path.expanduser(os.path.expandvars(ec2_ini_path))
         config.read(ec2_ini_path)
 
         # is eucalyptus?