block/nfs: fix naming of runtime opts

commit 94d6a7a7 accidentally left the naming of runtime opts and QAPI
scheme inconsistent. As one consequence passing of parameters in the
URI is broken. Sync the naming of the runtime opts to the QAPI
scheme.

Please note that this is technically backwards incompatible with the 2.8
release, but the 2.8 release is the only version that had the wrong naming.
Furthermore release 2.8 suffered from a NULL pointer dereference during
URI parsing.

Fixes: 94d6a7a7
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Lieven <pl@kamp.de>
Message-id: 1485942829-10756-3-git-send-email-pl@kamp.de
[mreitz: Fixed commit message]
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>