Remove Oozie external DB properties from Blueprint Export

This patch resolves bug AMBARI-7507.

Some Oozie properties related to using an external MySQL
  Database (oozie_existing_mysql_host, oozie.service.JPAService.jdbc.url)
  are currently appearing in an exported Blueprint with
  hostname information included.  This is incorrect, since
  the hostname information should be completely removed or
  masked in an exported Blueprint.  Having a reference to a
  given hostname in this scenario is not very useful, since the
  Blueprint may be applied to a completely different set of
  machines.

These Oozie properties generally will only be set to
  either a default, in-memory DB, or to an external
  MYSQL server instance.  This means that the normal
  PropertyUpdater processing won't really apply to
  these two properties.

This patch fixes this problem by creating a new
  PropertyUpdater type, which is only responsible
  for tracking these two property types, and marking
  them as properties that will not be included
  in an exported Blueprint.

This patch also adds a processing method to
  handle any properties that use this new
  PropertyUpdater, and this processing method
  will remove these registered properties
  during the export process.

This patch also adds a unit test to verify this change.