Error handling in swift objectstorage driver

[Swathi Gangisetty]

Error handling in swift driver's credential verification path is masking the original error

https://github.com/anchore/anchore-engine/blob/master/anchore_engine/subsys/object_store/drivers/swift.py#L75

Log snippet

File "/usr/local/lib/python3.8/site-packages/anchore_engine/subsys/object_store/drivers/swift.py", line 75, 
in _check_creds elif resp.get("error") and resp.get("error").http_status in [401, 403]: 
AttributeError: 'SSLError' object has no attribute 'http_status'

#1140 was opened to address the issue