qcow2: Refcount checking code cleanup (Kevin Wolf)

This is purely cosmetical changes to make the code easier to read. Move L2
table processing from a deeply nested block to its own function, add some
comments.

Patch v2: Fix misplaced bracket causing false positives

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@7216 c046a42c-6fe2-441c-8c8c-71466251a162
