Increase the default limit number of loop devices

These are only used in certain cases like windows sysprep.  In
the case where you need to do one of these functions across a
large number of virtual machines, you can quickly run out of
loop devices and fail.  An increase has very little overhead
(if any) and solves this problem.

Increase from 8 to 256 loop devices
If users need more or want less, it can be changed by changing
the kernel boot parameter loop_max

rhbz#883391

Change-Id: If47cdbc170736110d75d3baf28c850cd4b1876a2
Signed-off-by: Mike Burns <mburns@redhat.com>