tests: uml: Request non-raw serial ports

tests: uml: Request non-raw serial ports

When the serial ports are set into raw mode on stdio (fd:0,fd:1)
then Ctrl-C is sort of passed through, but not effective. Request
non-raw mode to avoid that and let us cancel test execution with
Ctrl-C properly (both in parallel-vm.py and vm-run.sh cases).

Note that this requires a currently out-of-tree patch, but so
does the virtual time. If the patch is not applied, the command
line argument is ignored.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>