qemu-io: Exit with error when a command failed

qemu-io: Exit with error when a command failed

Currently, qemu-io basically always returns success when it gets to
interactive mode (so once the whole command line has been parsed; even
before the commands on the command line are interpreted).  That is not
very useful.

This patch makes qemu-io return failure when any of the executed
commands failed.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1519617
Signed-off-by: Max Reitz <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Message-id: 20180509194302[email protected]
Signed-off-by: Max Reitz <[email protected]>