Install unzip explicitly for completeness

We need unzip for npm tasks, and we're getting it transitively
via Recommends from the zip package. However, since unzip is
important, go ahead and be explicit.

Change-Id: I6ead5517d43d8bbd2e306f451383f73cd600dd40
diff --git a/roles/install-build-essential/tasks/main.yaml b/roles/install-build-essential/tasks/main.yaml
index a83517c..9668b7f 100644
--- a/roles/install-build-essential/tasks/main.yaml
+++ b/roles/install-build-essential/tasks/main.yaml
@@ -4,4 +4,5 @@
     name:
       - build-essential
       - zip
+      - unzip
     state: present