Add instructions to load nbd kernel module on SUSE based systems

This solves the following issue when trying to start a new instance.

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2014-10-14 13:19:32.791 20021 ERROR nova.virt.disk.mount.nbd [req-38f661b6-
b192-423b-9f41-2c28b9372af1 None] nbd module not loaded
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Change-Id: I1bc5ab6d0b40d70cb19ada660d1b0b02b7903ba3
Merge "Add instructions to load nbd kernel module on SUSE based systems"