yum-minimal: do not configure eth0 & eth1 for DHCP automatically

Add an environment variable to control the creation of eth0/1
interface enablement scripts.

With a tool such as glean, the presence of these scripts will indicate
the interface is configured and configuration-drive settings will not
be applied.  This means in a non-dhcp situation like on Rackspace,
network is broken.

On Fedora, where later systemd provides "predictable network interface
names" [1] eth0 & eth1 ironically aren't predictable so this just
confuses things.  You really need cloud-init or glean or something to
bring up your interfaces in a sane fashion.

This maintains the status-quo on centos-minimal, but disables creation
for fedora-minimal.

[1] http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/

Change-Id: I3f1ffeb6de3b1f952292a144efab9554f7f99a5f

elements/centos-minimal/README.rst

@@ -12,3 +12,10 @@ flag to disk-image-create when using this element.
 The `DIB_OFFLINE` or more specific `DIB_YUMCHROOT_USE_CACHE`
 variables can be set to prefer the use of a pre-cached root filesystem
 tarball.
+
+By default, `DIB_YUM_MINIMAL_CREATE_INTERFACES` is set to enable the
+creation of `/etc/sysconfig/network-scripts/ifcfg-eth[0|1]` scripts to
+enable DHCP on the `eth0` & `eth1` interfaces.  If you do not have
+these interfaces, or if you are using something else to setup the
+network such as cloud-init, glean or network-manager, you would want
+to set this to `0`.

elements/centos-minimal/environment.d/10-centos-distro-name.bash

@@ -1,2 +1,6 @@
 export DISTRO_NAME=centos
 export DIB_RELEASE=${DIB_RELEASE:-7}
+
+# by default, enable DHCP configuration of eth0 & eth1 in network
+# scripts.  See yum-minimal for full details
+export DIB_YUM_MINIMAL_CREATE_INTERFACES=${DIB_YUM_MINIMAL_CREATE_INTERFACES:-1}

elements/yum-minimal/README.rst

@@ -12,3 +12,7 @@ Ubuntu and Debian. Nothing additional is needed on Fedora or CentOS.
 The `DIB_OFFLINE` or more specific `DIB_YUMCHROOT_USE_CACHE`
 variables can be set to prefer the use of a pre-cached root filesystem
 tarball.
+
+If you wish to have DHCP networking setup for eth0 & eth1 via
+/etc/sysconfig/network-config scripts/ifcfg-eth[0|1], set the
+environment variable `DIB_YUM_MINIMAL_CREATE_INTERFACES` to `1`.

elements/yum-minimal/install.d/10-base-networking

@@ -28,10 +28,17 @@ NETWORKING_IPV6=yes
 NOZEROCONF=yes
 EOF
 
-for interface in eth0 eth1; do
+# If you want eth0 and eth1 created as DHCP based interfaces, enable
+# this.  You don't want this if systemd is going to call the
+# interfaces on the real system something else, or if you're using a
+# network-manager like cloud-init, glean or network-manager that will
+# handle the interfaces dynamically.
+if [[ "${DIB_YUM_MINIMAL_CREATE_INTERFACES:-0}" -eq "1" ]]; then
+    for interface in eth0 eth1; do
         cat << EOF | tee /etc/sysconfig/network-scripts/ifcfg-$interface > /dev/null
 DEVICE=$interface
 BOOTPROTO=dhcp
 ONBOOT=on
 EOF
-done
+    done
+fi