runqemu: only boot ramfs when specified

This can fix a problem:
IMAGE_FSTYPES += "iso"
$ bitbake core-image-minimal
$ runqemu qemux86

It may boot core-image-minimal-initramfs rather than core-image-minimal, this
is not what we want usually. This patch makes it avoid booting ramfs when there
are other choices, or when it is specified, for example, "runqemu qemux86 ramfs"

(From OE-Core rev: 614bde6774f4dfd414066bbaf75ed422943e37ab)

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

scripts/runqemu

@@ -660,7 +660,15 @@ class BaseConfig(object):
                 logger.info('Running %s...' % cmd)
                 qbs = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE).stdout.read().decode('utf-8')
                 if qbs:
-                    self.qemuboot = qbs.split()[0]
+                    for qb in qbs.split():
+                        # Don't use initramfs when other choices unless fstype is ramfs
+                        if '-initramfs-' in os.path.basename(qb) and self.fstype != 'cpio.gz':
+                                continue
+                        self.qemuboot = qb
+                        break
+                    if not self.qemuboot:
+                        # Use the first one when no choice
+                        self.qemuboot = qbs.split()[0]
                     self.qbconfload = True
 
         if not self.qemuboot: