qemuBlockReopenFormatMon: Adapt to new argument format of 'blockdev-reopen'

qemuBlockReopenFormatMon: Adapt to new argument format of 'blockdev-reopen'

This function was added prior 'blockdev-reopen' being stable and qemu
changed the arguments to actually contain an array of block node
definitions to reopen.

In our case we are just changing between read-only and read-write modes
and thus we can keep operating on the nodes one-by-one.

Modify the code to add the wrapper array.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>