Changelog:
===========
Prevent returning an empty list for ClassDef.slots() when the mro list contains one class & it is not object.
Prevent a crash when inferring calls to str.format with inferred arguments
Infer the length argument of the random.sample function.
Catch ValueError when indexing some builtin containers and sequences during inference.
Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
