Update the apt indices before installing packages

Images may sometimes ship with outdated package data, so installing
something in that state could lead to failures when a cached index
refers to a package version which is no longer available from the
repository. Force an update of the indices first in order to avoid
that potential failure condition.

Change-Id: I54bd13f77ea4e53d11efbc3208a878c331ea3291
diff --git a/playbooks/base-test/pre.yaml b/playbooks/base-test/pre.yaml
index d461287..8125025 100644
--- a/playbooks/base-test/pre.yaml
+++ b/playbooks/base-test/pre.yaml
@@ -5,6 +5,9 @@
 
 - hosts: all
   tasks:
+    - name: Update apt cache
+      become: true
+      command: apt-get update
     - name: Install packages
       become: true
       package:
diff --git a/playbooks/base/pre.yaml b/playbooks/base/pre.yaml
index d461287..8125025 100644
--- a/playbooks/base/pre.yaml
+++ b/playbooks/base/pre.yaml
@@ -5,6 +5,9 @@
 
 - hosts: all
   tasks:
+    - name: Update apt cache
+      become: true
+      command: apt-get update
     - name: Install packages
       become: true
       package: