Improved search for unlocked system accounts
Improved search for unlocked system accounts

This patch adds a better check for system accounts that aren't
unlocked. The new logic meets the requirement of V-38496 from the
STIG better than the previous version. Only unlocked accounts with
UID < 500 will trigger the failure/violation.

Closes-Bug: 1550442

Change-Id: I18ccbd8e1cd7c311521d0ffdfcf6f46dbc4e395d

major/openstack-ansible-security,major/openstack-ansible-security