Fix missing argument to QemuImageInfo

set the default value for cmd_output to None. _parse
does work fine with None or empty string

Fixes LP# 1157412

Change-Id: Ib63f2fd227633b96db613ce29563d1929536819a
Merge "Fix missing argument to QemuImageInfo"
Merge remote-tracking branch 'm_src_repo/master' into build-temp