tools: Add a block-tap script for setting up tapdisks via tap-ctl

tools: Add a block-tap script for setting up tapdisks via tap-ctl

The blocktap library isn't really necessary; all the necessary functionality
is available via the tap-ctl binary.

To use:

script=block-tap,vdev=[whatever],target=vhd:/path/to/file.vhd

script=block-tap,vdev=[whatever],target=aio:/path/to/file.raw

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>