[JENKINS-13742] Field validation does not pass required query parameters
when some fields are specified in a nested Describable

# On branch master
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* src/main/java/com/collabnet/ce/webservices/CTFProject.java
  (getOrCreateDocumentFolder, verifyPath): strip file separators from beginning and end of path

* src/main/java/com/collabnet/ce/webservices/CollabNetApp.java
  (fromStapler): renamed overrideAuth to connectionFactory, the former is more descriptive,
  but the checkbox takes the name of the composite field.  Added RelativeParameter
  annotations to the other arguments. Also the password field may contain the encrypted
  form, so using Secret to transform into plaintext.

* src/main/java/hudson/plugins/collabnet/ConnectionFactory.java
  Add a fromStapler method so this can be used in validations that are internal to the
  composite field, such as the modified doCheckPassword method.

* src/main/java/hudson/plugins/collabnet/auth/CNAuthProjectProperty.java
  (doFillProjectItems): simplified by using getProjectList method.

* src/main/java/hudson/plugins/collabnet/browser/TeamForge.java
  (doFillProjectItems, doFillRepoItems): Added code to logoff the CTF session

* src/main/java/hudson/plugins/collabnet/tracker/CNTracker.java
  (doFillTrackerItems): Add a null check to avoid NPE, if auth data is not found

* src/main/java/hudson/plugins/collabnet/util/CNFormFieldValidator.java
  Several methods are modified to add null checks for the CollabNetAuth arg and to
  ensure the session is logged off.  Prior to this change some methods did one
  and others did the other and some did neither.

* src/main/java/hudson/plugins/collabnet/util/ComboBoxUpdater.java
  (getUsers): Add null check on CollabNetApp arg