doc: fix failure to make pdf output for project docs

The "make pdf" processing doesn't handle .svg files that were introduced
for the config option documentation.  Change these images to .png
instead.

The "make pdf" processing tools produce slightly different log output.
Tweak the "known issue" processing script (that removes messages from
the sphinx_build output for known issues that we can safely ignore.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/reference/config-options.rst

@@ -37,19 +37,19 @@ String
 
 .. comment These images are used in generated option documentation
 
-.. |icon-advanced| image:: images/Advanced.svg
+.. |icon-advanced| image:: images/Advanced.png
    :alt: Find this option on the Configurator's Advanced Parameters tab
-.. |icon-basic| image:: images/Basic.svg
+.. |icon-basic| image:: images/Basic.png
    :alt: Find this option on the Configurator's Basic Parameters tab
-.. |icon-not-available| image:: images/Not-available.svg
+.. |icon-not-available| image:: images/Not-available.png
    :alt: This is a hidden option and not user-editable using the Configurator
-.. |icon-post-launched-vm| image:: images/Post-launched-VM.svg
+.. |icon-post-launched-vm| image:: images/Post-launched-VM.png
    :alt: Find this option on a Configurator Post-launched VM tab
-.. |icon-pre-launched-vm| image:: images/Pre-launched-VM.svg
+.. |icon-pre-launched-vm| image:: images/Pre-launched-VM.png
    :alt: Find this option on a Configurator Pre-launched VM tab
-.. |icon-service-vm| image:: images/Service-VM.svg
+.. |icon-service-vm| image:: images/Service-VM.png
    :alt: Find this option on the Configurator Service VM tab
-.. |icon-hypervisor| image:: images/Hypervisor.svg
+.. |icon-hypervisor| image:: images/Hypervisor.png
    :alt: Find this option on the Configurator's Hypervisor Global Settings tab
 
 We use icons within an option description to indicate where the option can be