Finish QCOW version 2 and stop making it conditional.

We have a different ordering for the RC block(s) and L2 tables.
This is expected to be a non-issue, because everything is found
through file offsets in the corresponding RC table and L1 table.
Files that grow organically have RC blocks and L2 tables scattered
all over the place anyway.

The reason for the difference is that mkimg needs to be able to
write to a pipe. We can't seek forward and backward to fill in
the bits in non-sequential order.
Increase the memory disk size in the following testcases to avoid mount
failures, which would cause cascade failures in the rest of the test
run:

link/15.t, open/19.t, mkdir/11.t, mkfifo/11.t, symlink/11.t

Fail quickly in all of the testcases if mdconfig, mount, umount, etc
fails to avoid issues similar to this in the future

Submitted by: Casey Peel <cpeel@isilon.com>
MFC after: 2 weeks
X-MFC with: r272057
Sponsored by: EMC / Isilon Storage Division
Add baseline files for QCOW2.