Fix unit-test-docker proxy handling

This change introduces setting correct proxy setting for keyserver
resolution during docker build.

Testing:
- docker successfully builds and runs image behind corporate proxy

Change-Id: I15a2d09cc62f7405cc14a8e41c7863fee01548be
Signed-off-by: Adrian Ambrożewicz <adrian.ambrozewicz@intel.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index ccc4212..8230ee0 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -684,12 +684,15 @@
 
 # Special flags for proxying.
 proxy_cmd = ""
+proxy_keyserver = ""
 proxy_args = []
 if http_proxy:
     proxy_cmd = f"""
 RUN echo "[http]" >> {homedir}/.gitconfig && \
     echo "proxy = {http_proxy}" >> {homedir}/.gitconfig
 """
+    proxy_keyserver = f"--keyserver-options http-proxy={http_proxy}"
+
     proxy_args.extend(
         [
             "--build-arg",
@@ -723,6 +726,7 @@
     ( apt-get install gpgv ubuntu-dbgsym-keyring || \
         ( apt-get install -yy dirmngr && \
           apt-key adv --keyserver keyserver.ubuntu.com \
+                      {proxy_keyserver} \
                       --recv-keys F2EDC64DC5AEE1F6B9C621F0C8CAB6595FDFF622 ) )
 
 # Parse the current repo list into a debug repo list