Support invoking qemu in command line and fix a test issue

The script uCore_run can now support invoking qemu in a command prompt
environment. The control hotkeys in qemu can be used to exit emulation
or enter qemu monitor, i.e.

    Ctrl-a x    Exit emulation
    Ctrl-a c    Enter qemu monitor

This patch also fixes the always-fail issue when using qemu 1.4.0. The
problem is that using the option '-gdb' twice no longer work.

Signed-off-by: Junjie Mao <eternal.n08@gmail.com>