Patch writexml for non standard XML DOM implementations

PyXML will replace the default DOM implementation and as a result, it
will reintroduce the broken writexml method that was present with python
versions before 2.7

Change-Id: I8847c344df2f7b2d76291a24cdb8e1a436ac87ec
Fixed referenced before assignment in zuul module

It was using a non-defined url variable and failed to me when running a
simple jenkins-jobs test -o ../outdir .

Change-Id: I56e6376de4972ea0f64bd8c81d6eb6d8f7f6d497
Signed-off-by: David Caro <dcaroest@redhat.com>
Fix a broken include in the configuration documentation.

Change-Id: I803caea42365e44851068e510d5e698447aad73b
Use yaml local tags to support including files

Add support for local tags which are application specific to allow
including of other yaml files or code from scripts. Allows for code to
be maintained and tested as seperate files, as well as reduces
duplication of yaml code that cannot be macro'ed or easily templated by
including it from a common file.

Adds support for the following tags:
  'include' - load file as yaml code
  'include-raw' - load file as data (for scripts)
  'include-raw-escaped' - load file as data with escaping braces '{}'
      as default for use with job-templates

Use configuration file options to provide a search path for the files.

- Test behaviour of yaml tags independent of any XML generation
  by comparing json result of yaml parsing to verify that certain
  tags do/don't recall the yaml.load() method.
- Add examples for the include tags via addition tests for YamlParser
  class

Inspired by
http://stackoverflow.com/questions/528281/how-can-i-include-an-yaml-file-inside-another

Change-Id: Ib90a07043112d4739d6529ceddbc9817668bcec0
Merge "Use yaml local tags to support including files"
Merge "Fixed referenced before assignment in zuul module"
Merge "Fix a broken include in the configuration documentation."
Merge "Patch writexml for non standard XML DOM implementations"