runqemu: standardize ability to specify custom qemu/kenel boot options

runqemu: standardize ability to specify custom qemu/kenel boot options

The old manner of specifying custom options to QEMU in this script
using angle brackets was a frequent source of confusion. Meanwhile,
Otavio Salvador added a decent method of specifying custom kernel
boot options to this script. This patch documents the bootparams
option and adds a similar way of specifying custom QEMU options
using qemuparams="".

This fixes [YOCTO #1019]

(From OE-Core rev: 1038df14a96d789b3f9e9e1692305ba1fea67886)

Signed-off-by: Scott Garman <scott.a.garman@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>