fix 1138 forcing cryptography version 2.5 or higher

Some fixing in devops-stages/stage-build
Use US18.04 for Dockerfile used for devops-stages

Change-Id: Ia2cb09e21efe11a22013de48b2404f5ead949a71
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>