Fix various substitution issues

This PS solves the following issues for which only minor changes
were needed:

1) Using copy.copy() around the substitution value passed in
   to jsonpath_replace so as to avoid updating the substitution
   entry referentially which was happening before this change,
   causing future substitutions using that entry to fail or
   behaving unexpectedly.
2) Supporting non-string substitution values when a substitution
   pattern is provided: before this change, this was failing
   because calling re.sub() and passing in a non-string
   value causes an error to be thrown.
3) Adding better logging and error handling to
   deckhand.utils.jsonpath_replace to assist with debugging.

Unit tests are included for some of the scenarios above.

Change-Id: I8562d43a717f477e3297504c1522331b3a993f88

deckhand/engine/secrets_manager.py

@@ -215,8 +215,7 @@ class SecretsSubstitution(object):
                 except Exception as e:
                     LOG.error('Unexpected exception occurred while attempting '
                               'secret substitution. %s', six.text_type(e))
-                    raise errors.SubstitutionDependencyNotFound(
-                        details=six.text_type(e))
+                    raise errors.SubstitutionFailure(details=six.text_type(e))
 
         yield document