Add proxy support

It's not possible to build the Docker images behind a corporate
proxy. This change adds support to HTTP and HTTPS protocols for
creation of images.

Change-Id: Iabe675d86e2879270dda069179b7b854da0a93bd
Signed-off-by: Victor Morales <victor.morales@intel.com>
diff --git a/sdc-os-chef/sdc-frontend/Dockerfile b/sdc-os-chef/sdc-frontend/Dockerfile
index a59d868..17034ef 100644
--- a/sdc-os-chef/sdc-frontend/Dockerfile
+++ b/sdc-os-chef/sdc-frontend/Dockerfile
@@ -1,5 +1,14 @@
 FROM jetty:9.3.15-jre8
 
+ARG HTTP_PROXY
+ARG HTTPS_PROXY
+
+ENV HTTP_PROXY  ${HTTP_PROXY}
+ENV HTTPS_PROXY ${HTTPS_PROXY}
+
+RUN if [ ! -z ${HTTP_PROXY} ]; then echo "Acquire::http::proxy  \"${HTTP_PROXY}\";" >> /etc/apt/apt.conf; fi && \
+    if [ ! -z ${HTTPS_PROXY} ]; then echo "Acquire::https::proxy \"${HTTPS_PROXY}\";" >> /etc/apt/apt.conf; fi 
+
 RUN apt-get -y update
 RUN apt-get -y install apt-utils
 RUN apt-get -y install curl