Add new multipath element

Provide an element that provides multipath support allowing a user to
configure multiple I/O paths to storage devices. Typically used with
SAN storage arrays.

Change-Id: I2f970399109b1396c25cb6e2ef2906310d04c5f8

elements/multipath/README.md

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+Add multipath-tools to built images
+===================================
+
+This element adds multipath-tools to the image. These tools manage the kernel
+device mapper based multipath support.
+
+See [multipath-tools](http://christophe.varoqui.free.fr/) for more information.
+
+This element installs multipath with a default configuration that disables
+multipath for all block devices. The user can then customise the config to suit
+their environment.

elements/multipath/files/multipath.conf

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+blacklist {
+    devnode "*"
+}

elements/multipath/install.d/90-multipath

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+#!/bin/bash
+# Copyright 2014 Hewlett-Packard Development Company, L.P.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+set -eux
+
+install-packages -m multipath multipath_tools_package
+
+# default to blacklisting all devices to avoid the installation of multipath
+# changing the default behaviour of the system.
+install -m 0644 -o root -g root $(dirname $0)/../files/multipath.conf /etc/multipath.conf
+

elements/multipath/pkg-map

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+{
+  "family": {
+    "redhat": {
+      "multipath_tools_package": "device-mapper-multipath"
+    }
+  },
+  "default": {
+    "multipath_tools_package": "multipath-tools"
+  }
+}