Mask node.session.auth.password in volume.py _run_iscsiadm debug logs

The iscsi_command object passed to _run_iscsiadm can contain passwords
that get logged at debug level, so we need to sanitize the message
getting logged.

Adds a test to ensure the logged message is properly sanitized.

Closes-Bug: #1320028

Change-Id: I33f1a5b698368504721b41e56266162a713b3ce6
Merge "Mask node.session.auth.password in volume.py _run_iscsiadm debug logs"