ermine-breeder: Fix to reset QEMU_OPT before calling minc-moult
ermine-breeder: Fix to reset QEMU_OPT before calling minc-moult

This resets QEMU_OPT by user-defined options after calling
prepare_arch, because prepare_arch appends some arch options
to QEMU_OPT aind minc-moult calls prepare_arch again.
This means QEMU_OPT will have 2 set of the arch options.
Let's clean it up before calling minc-moult.

Signed-off-by: Masami Hiramatsu <c722459ed079dc74f5b0af068882bc5c41a907a2@linaro.org>

mhiramat/mincs