Port items from instack-undercloud

Currently we leverage the overcloud-full and pip-and-virtualenv-override
elements from instack-undercloud during image building. In order to
remove instack-undercloud as a dependency, we need to move these items
elsewhere.  Since you cannot have overlapping names, the overcloud-full
element functionality has been moved to overcloud-base and
overcloud-compute with the file names 50 being replaced with 51.
The pip-and-virtualenv-override elements has been renamed to
override-pip-and-virtualenv.  A subsequent set of patches will be posted
to tripleo-common to remove instack-undercloud from the image building
path and an update to the elements required when building images.

Change-Id: I1de0b6421ef455ef58c0146da7fe52c35682b395
Related-Blueprint: remove-instack-undercloud

elements/overcloud-base/install.d/51-persistent-journal

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+set -eu
+set -o pipefail
+
+# Enable persistent logging for the systemd journal
+mkdir -p /var/log/journal

elements/overcloud-compute/post-install.d/51-remove-libvirt-default-net

@@ -0,0 +1,6 @@
+#!/bin/bash
+
+set -eux
+set -o pipefail
+
+rm -f /etc/libvirt/qemu/networks/autostart/default.xml

elements/override-pip-and-virtualenv/README.md

@@ -0,0 +1,4 @@
+This element will override the behavior from the pip-and-virtualenv element
+from tripleo-image-elements so that python-pip and python-virtualenv are never
+installed.
+

elements/override-pip-and-virtualenv/element-provides

@@ -0,0 +1 @@
+pip-and-virtualenv