[dvsim/testplan] Fix the rendered testplan
[dvsim/testplan] Fix the rendered testplan

There were some mistakes made causing the testplan to be rendered
poorly:
- The list of tests are not exhibiting the line breaks correctly
  - Only thing that works is the addition of <br> tags
- The decription is also mis-rendered if converted to HTML after
tabulate step (some formatting items are not getting converted from
markdown text to html)
  - Need to convert to html first and then process the tabulate to do
  this right.

Signed-off-by: Srikrishna Iyer <2803d640feace36379942447842f26c7747b4dc3@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan