Previously, runqemu grep root=/dev/sd or root=/dev/hd on the image, and
would use vda if no grep result, now we have set QB_DRIVE_TYPE to
"/dev/sd" by default, and the device will be /dev/sda, so use sda to
replace vda in the test case.
(From OE-Core rev: a722016df3f452f7a870157a99a1abb7d97d8280)
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>