Add fixref to XCCDF generation to be compatible with STIG Viewer 3.x

[rlakey]

When importing an XCCDF file generated in Vulcan into the new STIG Viewer 3 the Fix Text does not display.

Screenshot where fix text is not shown.

In the xml it looks like this when not working.

<fixtext>Navigate to and open:

/etc/audit/rules.d/audit.STIG.rules

Add or update the following lines:

-w /usr/sbin/useradd -p x -k useradd
-w /usr/sbin/groupadd -p x -k groupadd

At the command line, run the following command to load the new audit rules:

# /sbin/augenrules --load

Note: An "audit.STIG.rules" file is provided with this guidance for placement in "/etc/audit/rules.d" that contains all rules needed for auditd.</fixtext>

Updating the above to have a fixref id allows it to be displayed.

<fixtext fixref="F-PHTN-50-000003_fix">Navigate to and open:

/etc/audit/rules.d/audit.STIG.rules

Add or update the following lines:

-w /usr/sbin/useradd -p x -k useradd
-w /usr/sbin/groupadd -p x -k groupadd

At the command line, run the following command to load the new audit rules:

# /sbin/augenrules --load

Note: An "audit.STIG.rules" file is provided with this guidance for placement in "/etc/audit/rules.d" that contains all rules needed for auditd.</fixtext>

Suggest adding this new attribute to the fixtext node with the syntax fixref="F-<STIG ID>_fix" for example fixref="F-PHTN-50-000003_fix".

[smarlaku820]

PR - https://github.com/mitre/vulcan/pull/608