Fix support for obsolete format of pre-scm-buildstep

'pre-scm-buildstep' wrapper has two modes:
1. Older: no 'buildsteps' element is specified. Build steps is a list under
   wrapper name. For example:

    - pre-scm-buildstep:
      - shell: echo hello
      - shell: echo bye

2. Newer: build steps specified inside 'buildsteps' mapping element:

    - pre-scm-buildsteps:
        buildsteps:
        - shell: echo hello
        - shell: echo bye

But, when 'preSCMbuildstep' plugin version is equal or higher 0.3, and first
mode is used, it fails.

Fix that.

Change-Id: I010d9f6c5e06ccd8c2723026aae2c60f79917ff4

jenkins_jobs/modules/wrappers.py

@@ -1833,7 +1833,7 @@ def pre_scm_buildstep(registry, xml_parent, data):
     for step in stepList:
         for edited_node in create_builders(registry, step):
             bs.append(edited_node)
-    if version >= pkg_resources.parse_version("0.3"):
+    if version >= pkg_resources.parse_version("0.3") and not isinstance(data, list):
         mapping = [("failOnError", "failOnError", False)]
         helpers.convert_mapping_to_xml(bsp, data, mapping, fail_required=True)
 

tests/wrappers/fixtures/pre-scm-buildstep-no-buildsteps.plugins_info.yaml

@@ -0,0 +1,3 @@
+- longName: 'Pre SCM BuildStep Plugin'
+  shortName: 'preSCMbuildstep'
+  version: "0.3"

tests/wrappers/fixtures/pre-scm-buildstep-no-buildsteps.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <buildWrappers>
+    <org.jenkinsci.plugins.preSCMbuildstep.PreSCMBuildStepsWrapper>
+      <buildSteps>
+        <hudson.tasks.Shell>
+          <command>#!/bin/bash
+echo &quot;Doing something cool&quot;
+</command>
+        </hudson.tasks.Shell>
+        <hudson.tasks.Shell>
+          <command>#!/bin/zsh
+echo &quot;Doing something cool with zsh&quot;
+</command>
+        </hudson.tasks.Shell>
+      </buildSteps>
+    </org.jenkinsci.plugins.preSCMbuildstep.PreSCMBuildStepsWrapper>
+  </buildWrappers>
+</project>

tests/wrappers/fixtures/pre-scm-buildstep-no-buildsteps.yaml

@@ -0,0 +1,8 @@
+wrappers:
+  - pre-scm-buildstep:
+      - shell: |
+          #!/bin/bash
+          echo "Doing something cool"
+      - shell: |
+          #!/bin/zsh
+          echo "Doing something cool with zsh"