test: add a testcase for dynamic logs

test: add a testcase for dynamic logs

Update the logs test to also validate the dynamic log framework.
For now, also keep the old way using the static USER type.

Validated with:

   # build/app/test --no-huge
   ...
   RTE>>logs_autotest
   == dynamic log types
   error message
   critical message
   critical message
   error message
   == static log types
   TESTAPP1: error message
   TESTAPP1: critical message
   TESTAPP2: critical message
   TESTAPP1: error message
   Test OK

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>