Use cElementTree

Same code as used in Salt.
Salt Cloud depends on Salt, use its _compat.py
Merge pull request #880 from holmboe/etree-compat

Use cElementTree if available
IamInstanceProfile settings also require spot_prefix when creating spot instances.
Merge pull request #881 from lusid/develop

IamInstanceProfile settings also require spot_prefix when creating spot instances.
Added "type" parameter to spot_config so persistent spots could be created by adding "type": "persistent". Defaults to "type": "one-time" as before.
Merge pull request #882 from lusid/develop

Added ability to create persistent spot instances on EC2
Removing stray pprint import
Merge pull request #884 from techhat/nova

Removing stray pprint import
Remove duplicate entries in documentation

The two release notes are also included in releases/index thus they
appeared twice in the documentation.
Merge pull request #885 from holmboe/doc-release-duplicate

Remove duplicate entries in documentation
Fix path to salt-cloud man page
Merge pull request #886 from holmboe/doc-cli-man

Fix path to salt-cloud man page
Add salt-cloud(1) to index
Merge pull request #887 from holmboe/doc-man-index

Add salt-cloud(1) to index
Fix RST literal blocks for CLI examples
Merge pull request #888 from holmboe/rst-literal-blocks

Fix RST literal blocks for CLI examples
Add a function to construct AWS parameters from configuration data; BlockDeviceMapping accepts all allowed configuration keywords -- This makes it possible to change the size of the root device.
Avoid hardcode the index of the BlockDeviceMappings. If the target device is aleady in the list, modify its configuration directly. Otherwise, add a new BlockDeviceMapping with a proper index.
Add doc about changing the size of the root device in AWS