Add screen, required by kind-voltha builds

Change-Id: I73eca239eca0dfd7b19867f672b00b3109cc529c
diff --git a/packer/provision/basebuild.sh b/packer/provision/basebuild.sh
index 08c7a5a..1bba231 100644
--- a/packer/provision/basebuild.sh
+++ b/packer/provision/basebuild.sh
@@ -115,6 +115,7 @@
         python-urllib3 \
         python3-dev \
         ruby \
+        screen \
         socat \
         ssh \
         sshpass \