slapos_upgrader: Add script to upgrade only erp5_core

On certain scenarios, like the erp5_core has to be initially upgraded in separated transaction.

master/bt5/slapos_upgrader/SkinTemplateItem/portal_skins/slapos_upgrader/ERP5Site_upgradeERP5CoreBusinessTemplate.py

+template_tool = context.getPortalObject().portal_templates
+
+template_tool.updateRepositoryBusinessTemplateList(
+  template_tool.getRepositoryList())
+
+method_kw = {'bt5_list': ['erp5_core'],
+             'deprecated_after_script_dict': None,
+             'deprecated_reinstall_set': None,
+             'dry_run': False,
+             'delete_orphaned': False,
+             'keep_bt5_id_set': [],
+             'update_catalog': False}
+
+
+template_tool.upgradeSite(**method_kw)

master/bt5/slapos_upgrader/SkinTemplateItem/portal_skins/slapos_upgrader/ERP5Site_upgradeERP5CoreBusinessTemplate.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="PythonScript" module="Products.PythonScripts.PythonScript"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>Script_magic</string> </key>
+            <value> <int>3</int> </value>
+        </item>
+        <item>
+            <key> <string>_bind_names</string> </key>
+            <value>
+              <object>
+                <klass>
+                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
+                </klass>
+                <tuple/>
+                <state>
+                  <dictionary>
+                    <item>
+                        <key> <string>_asgns</string> </key>
+                        <value>
+                          <dictionary>
+                            <item>
+                                <key> <string>name_container</string> </key>
+                                <value> <string>container</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_context</string> </key>
+                                <value> <string>context</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_m_self</string> </key>
+                                <value> <string>script</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_subpath</string> </key>
+                                <value> <string>traverse_subpath</string> </value>
+                            </item>
+                          </dictionary>
+                        </value>
+                    </item>
+                  </dictionary>
+                </state>
+              </object>
+            </value>
+        </item>
+        <item>
+            <key> <string>_params</string> </key>
+            <value> <string></string> </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>ERP5Site_upgradeERP5CoreBusinessTemplate</string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+</ZopeData>