qcow2: Fix error path for unknown incompatible features

qcow2's report_unsupported_feature() had two bugs: A 32 bit truncation
would prevent feature table entries for bits 32-63 from being used, and
it could assign errp multiple times if there was more than one unknown
feature, resulting in an error_set() assertion failure.

Fix the truncation, make sure to set the error exactly once and add a
qemu-iotests case for it.

This fixes https://bugs.launchpad.net/qemu/+bug/1342704/

Reported-by: Maria Kustova <maria.k@catit.be>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
block: Add Error argument to bdrv_refresh_limits()

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
raw-posix: Fail gracefully if no working alignment is found

If qemu couldn't find out what O_DIRECT alignment to use with a given
file, it would run into assert(bdrv_opt_mem_align(bs) != 0); in block.c
and confuse users. This adds a more descriptive error message for such
cases.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
qemu-iotests: fix 028 failure due to disk image path

The disk image path is echoed by QEMU's readline when the "drive_backup
disk ${TEST_IMG}.copy" HMP command is issued.  Unfortunately it is very
hard to filter out the path due to readline's character-by-character
output (with terminal escape sequences).  Just redirect this command to
/dev/null for now.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>