Add verbose logging via KASMVNC_VERBOSE_LOGGING env var

Running "KASMVNC_VERBOSE_LOGGING=1 builder/test-deb debian buster" will
turn on verbose logging of kasmvncserver.

builder/test-rpm

@@ -10,5 +10,8 @@ docker build --build-arg \
   KASMVNC_PACKAGE_DIR="build/${os}_${os_codename}" \
   -t kasmvnctester_${os}:$os_codename \
   -f dockerfile.${os}_${os_codename}.rpm.test .
-echo docker run -it -p 443:8443 --rm -e "VNC_USER=foo" -e "VNC_PW=foobar" \
+
+docker run -it -p 443:8443 --rm \
+  -e KASMVNC_VERBOSE_LOGGING=$KASMVNC_VERBOSE_LOGGING \
+  -e "VNC_USER=foo" -e "VNC_PW=foobar" \
   kasmvnctester_${os}:$os_codename