Add missing sys imports to psu_base and fan_drawer_base

[spilkey-cisco]

Description

Import sys in modules where it was missing and attempted to be referenced. Found it missing in psu_base.py and fan_drawer_base.py.

Motivation and Context

sys.stderr.write is used in default API definitions within psu_base.py and fan_drawer_base.py. When an exception is caught within these APIs, they will throw NameError: name 'sys' is not defined when trying to use the sys module without first importing it. Issue was originally found for PSUs, but also exists within fan_drawer_base.

How Has This Been Tested?

Test code demonstrating the issue and the fix after importing sys

>>> def test(index):
...     l = []
...     try:
...         return l[index]
...     except IndexError:
...         sys.stderr.write('Index out of range\n')
...     return None
...
>>> test(1)
Traceback (most recent call last):
  File "<stdin>", line 4, in test
IndexError: list index out of range

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in test
NameError: name 'sys' is not defined
>>> import sys
>>> test(1)
Index out of range

Additional Information (Optional)

This fix should go into all active branches, especially master, 202205, and 202012.

[gechiang]

LGTM