selftest/runqemu.py: add it to test runqemu

selftest/runqemu.py: add it to test runqemu

Usage:
$ oe-selftest -r runqemu

Current test cases:
$ runqemu nographic qemux86-64
$ runqemu nographic qemux86-64 ext4
$ runqemu nographic qemux86-64 iso
$ runqemu nographic core-image-minimal
$ runqemu nographic core-image-minimal vmdk
$ runqemu nographic core-image-minimal vdi
$ runqemu nographic tmp/deploy/images/qemux86-64
$ runqemu nographic tmp/deploy/images/qemux86-64 hddimg
$ runqemu nographic qemux86-64 slirp
$ runqemu nographic qemux86-64 slirp qcow2
$ runqemu nographic tmp/deploy/images/qemux86-64/core-image-minimal-qemux86-64.qemuboot.conf
$ runqemu nographic tmp/deploy/images/qemux86-64/core-image-minimal-qemux86-64.ext4

Need more later:
- Test initramfs
- Test nfs
- Test when set DEPLOY_DIR_IMAGE and OECORE_NATIVE_SYSROOT
- And others which similate runqemu runs on SDK and eSDK.

[YOCTO #10249]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>