Disable deltarpm for CentOS and Fedora

deltarpm is useful when the bottleneck is the network throughput
on long-lived instances where you need to *update* packages that
are already installed.
It also requires the mirrors we are using to mirror the drpm packages
which is not currently done in our infrastructure.

Let's disable deltarpm as it's not suited to our use case.

Change-Id: Ibf3b6093496375efda26f46eaf90438af0adb394

roles/configure-mirrors/tasks/mirror/CentOS.yaml

@@ -11,3 +11,15 @@
     - etc/yum.repos.d/epel.repo
   notify:
     - Update yum cache
+
+# http://dnf.readthedocs.io/en/latest/conf_ref.html#options-for-both-main-and-repo
+# deltarpm is useful when the bottleneck is the network throughput.
+# It also requires additional drpm packages to be hosted by the mirrors which
+# is not done by default.
+- name: Disable deltrarpm
+  become: yes
+  ini_file:
+    path: /etc/yum.conf
+    section: main
+    option: deltarpm
+    value: 0

roles/configure-mirrors/tasks/mirror/Fedora.yaml

@@ -11,3 +11,15 @@
     - etc/yum.repos.d/fedora-updates.repo
   notify:
     - Update dnf cache
+
+# http://dnf.readthedocs.io/en/latest/conf_ref.html#options-for-both-main-and-repo
+# deltarpm is useful when the bottleneck is the network throughput.
+# It also requires additional drpm packages to be hosted by the mirrors which
+# is not done by default.
+- name: Disable deltrarpm
+  become: yes
+  ini_file:
+    path: /etc/dnf/dnf.conf
+    section: main
+    option: deltarpm
+    value: "false"