qemu-iotests: filter QEMU monitor \r\n

SMTP does not preserve newlines.  This is normally not a problem if the
email body uses DOS or UNIX newlines consistently.  In 051.out we mix
UNIX newlines with DOS newlines (since QEMU monitor output uses \r\n).

This patch filters the QEMU monitor output so the golden master file
uses UNIX newlines exclusively.

The result is that patches touching 051.out will apply cleanly without
mangling newlines after this commit.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>