signal.signal should not be used in library code

[Song-Zhiyi]

at alibabacloud_credentials/provider/ecs_ram_role.py:73-74

signal.signal() is used to register cleanup hooks for ram role rotation service.

It will add unexpected behavior to end user's application as library code is touching a global resource (the signal handling routines).
It is messing up with user's own signal handling logics.

Please avoid hooking into signals in library code, this is anti-pattern in library code.