Apply defaults to job-templates parameters

I had the use case of a lot of projects sharing the same job template
that uses a lot of variables.  That requires each project to define all
the variables even if they are mostly identical.

This patch propose to define varialbes as 'defaults' and have them
applied in the job-template magically (oneline diffs always have that
feeling to me).

So instead of:

- project:
    name: project1
    arch: amd64
    builder: debuild
    lintian: true
    jobs:
     - '{name}-build-{arch}'

And so on ...

I can just:

- defaults:
    name: sanebuild

- project:
    name: project1
    defaults: sanebuild
    jobs:
     - '{name}-build-{arch}'

And override the arch as needed either in the project or by passing it
to the job.

Without this patch, the provided yamlparser fixture
template_honor_defaults.yaml would raise:

    arch parameter missing to format echo Build arch {arch}.
    Given: {'': '', 'jobs': ['build-{arch}'], 'name': 'project-name'}

Change-Id: Ida1e27eb47356d9cae42175743bd2fd52eb9d869

doc/source/definition.rst

@@ -108,6 +108,8 @@ If you need several jobs defined that are nearly identical, except
 perhaps in their names, SCP targets, etc., then you may use a Job
 Template to specify the particulars of the job, and then use a
 `Project`_ to realize the job with appropriate variable substitution.
+Any variables not specified at the project level will be inherited from
+the `Defaults`_.
 
 A Job Template has the same syntax as a `Job`_, but you may add
 variables anywhere in the definition.  Variables are indicated by
@@ -298,6 +300,12 @@ definitions unless they specify a different Default object with the
 
 Will set the job description for every job created.
 
+You can define variables that will be realized in a `Job Template`.
+
+.. literalinclude::  /../../tests/yamlparser/fixtures/template_honor_defaults.yaml
+
+Would create jobs ``build-i386`` and ``build-amd64``.
+
 .. _advanced:
 
 Advanced

jenkins_jobs/builder.py

@@ -270,6 +270,7 @@ class YamlParser(object):
         checksums = set([])
         for values in itertools.product(*dimensions):
             params = copy.deepcopy(project)
+            params = self.applyDefaults(params)
 
             expanded_values = {}
             for (k, v) in values:

tests/yamlparser/fixtures/template_honor_defaults.xml

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <actions/>
+  <description>&lt;!-- Managed by Jenkins Job Builder --&gt;</description>
+  <keepDependencies>false</keepDependencies>
+  <blockBuildWhenDownstreamBuilding>false</blockBuildWhenDownstreamBuilding>
+  <blockBuildWhenUpstreamBuilding>false</blockBuildWhenUpstreamBuilding>
+  <concurrentBuild>false</concurrentBuild>
+  <canRoam>true</canRoam>
+  <properties/>
+  <scm class="hudson.scm.NullSCM"/>
+  <builders>
+    <hudson.tasks.Shell>
+      <command>echo Build arch amd64.</command>
+    </hudson.tasks.Shell>
+  </builders>
+  <publishers/>
+  <buildWrappers/>
+</project>
+<BLANKLINE>
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <actions/>
+  <description>&lt;!-- Managed by Jenkins Job Builder --&gt;</description>
+  <keepDependencies>false</keepDependencies>
+  <blockBuildWhenDownstreamBuilding>false</blockBuildWhenDownstreamBuilding>
+  <blockBuildWhenUpstreamBuilding>false</blockBuildWhenUpstreamBuilding>
+  <concurrentBuild>false</concurrentBuild>
+  <canRoam>true</canRoam>
+  <properties/>
+  <scm class="hudson.scm.NullSCM"/>
+  <builders>
+    <hudson.tasks.Shell>
+      <command>echo Build arch i386.</command>
+    </hudson.tasks.Shell>
+  </builders>
+  <publishers/>
+  <buildWrappers/>
+</project>

tests/yamlparser/fixtures/template_honor_defaults.yaml

@@ -0,0 +1,15 @@
+- defaults:
+    name: global
+    arch: 'i386'
+
+- project:
+    name: project-name
+    jobs:
+        - 'build-{arch}'
+        - 'build-{arch}':
+            arch: 'amd64'
+
+- job-template:
+    name: 'build-{arch}'
+    builders:
+        - shell: "echo Build arch {arch}."