Pass SSH_AUTH_SOCK through tools/bazel

This lets the aos downloader use local keys.

Change-Id: I7e7f46fde6d49cf5b3b8fbbb1e3c897816915d6f
diff --git a/tools/bazel b/tools/bazel
index 4589ca1..b4293a1 100755
--- a/tools/bazel
+++ b/tools/bazel
@@ -108,6 +108,10 @@
   ENVIRONMENT_VARIABLES+=(DISPLAY="${DISPLAY}")
 fi
 
+if [[ ! -z "${SSH_AUTH_SOCK+x}" ]]; then
+  ENVIRONMENT_VARIABLES+=(SSH_AUTH_SOCK="${SSH_AUTH_SOCK}")
+fi
+
 if [[ ! -z "${LOGNAME+x}" ]]; then
     ENVIRONMENT_VARIABLES+=(LOGNAME="${LOGNAME}")
 fi