args_from_args() to work with an instance of UserType

When the args_from_args() function fails to convert a value to a certain
type it tries to get the name of that type by using the __name__ attribute
of that type, UserType object instances doesn't have the __name__
attribute so the function fails when it tries to access it, this patch
makes WSME to check if it's an UserType instance before getting it's name.

Change-Id: If78ce0e642997421c97559cc28604421f5c03922
Closes-Bug: #1265590