build: add libssl-dev for ubuntu 16.04 and 18.04
build: add libssl-dev for ubuntu 16.04 and 18.04

The recent changes to Makefile lead to the lack of libssl-dev
dependency for ubuntu 16.04 and 18.04. Add libssl-dev to DEB_DEPENDS
variable for corresponding ubuntu version.

Type: fix

Change-Id: I42e0e4761d5ec377de71b11cccf747c7f55ca337
Signed-off-by: Jieqiang Wang <0d2338a8c8b15e8026f25a812965a9ac3057d6d3@arm.com>

chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp