Add python3-software-properties to basebuild.sh

Change-Id: I19f26d99b056f753c4422d501323cc0d345cb663
diff --git a/packer/provision/basebuild.sh b/packer/provision/basebuild.sh
index 5af75bc..36857b6 100644
--- a/packer/provision/basebuild.sh
+++ b/packer/provision/basebuild.sh
@@ -37,6 +37,7 @@
         python \
         python-pip \
         python-virtualenv \
+        python3-software-properties \
         rsync \
         ssh \
         zip