Return error on CMIS cancelCheckOut of document with cmis:versionLabel set to null

Steps to reproduce problem:

1. Create doc of type File with "Skip version increment"
2. Invoke CMIS cancelCheckOut Browser Binding operation on doc using curl

Current Result: doc is deleted
Improved Result: special error is returned indicating that a CMIS cancelCheckOut operation cannot be performed against a non-versioned document (which has no cmis:versionLabel)

Using the configuration property org.nuxeo.cmis.errorOnCancelCheckOutOfDraftVersion it's now possible to enable the returning of a versioning error when an attempt is made to call cancelCheckOut on a draft (live document with no version):

  <require>org.nuxeo.ecm.core.opencmis.configuration</require>
  <extension target="org.nuxeo.runtime.ConfigurationService" point="configuration">
    <property name="org.nuxeo.cmis.errorOnCancelCheckOutOfDraftVersion">true</property>
  </extension>