qemu: Add checks for blkdeviotune 'size_iops_sec' and adjust error

qemu: Add checks for blkdeviotune 'size_iops_sec' and adjust error

Seems the 'size_iops_sec' was a late add and the checks for whether
the field was defined, but unsupported and the maximum size of the
field were not being made.

Also, adjust blkdeviotune support error message for grammar, spelling
(paramater), and remove the "(need QEMU 1.7 or superior)".  None of
our other similar error messages list which QEMU version is required.

Signed-off-by: John Ferlan <jferlan@redhat.com>