addresses review comments, cleans up quite a few things.  most importantly:

    * change start sequence so that:
      * HA is known when the web console comes up (initPersistence before startWebApps)
      * launcher exits if persistence is misconfigured or if it fails to rebind

    * big tidy up of startup logging around persistence/HA
    * fix how jclouds integration tests inherit (couldn't find a nice way with any combo of @BeforeGroup / @BeforeMethod, so have just repeated all the test methods from supers)
    * support brooklyn.persistence.location.spec being set in brooklyn.properties
    * support brooklyn.persistence.backup.required (note, this defaults to false in obj store, but we seem to be pretty good about not clobbering things; even so, some prod usage may want versioning on the obj store)
    * clean up how persistence store initialization (prepare) is done
    * refactor of how object store items are written, with wrapper which handles locking, cutting code and fixing append for file and jclouds obj store
adds an xml memento serializer converter to intercept and restore the management context, as that is inserted in various places e.g. for DSL;
also several related fixes and tidies, moving anonymous inner classes to be named or statics, to make the memento xml a bit nicer.
updates xstream to 1.4.7. this is not needed but it seems a bit faster and friendlier (though i can't put my finger on either...).