Use busybox for udhcpd

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>
CA-142533: Don't keep fd open for /dev/vga_arbiter

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #1899 from jonludlam/udhcpd-xscore

Use busybox for udhcpd
Merge pull request #1918 from simonjbeaumont/ca-142533

CA-142533: Don't keep fd open for /dev/vga_arbiter
Update cli_frontend.ml

fix documentation for vif- and vdi mappings
Merge pull request #1922 from zaiyers/master

Update cli_frontend.ml