add support for persisting to object store

READY FOR REVIEW - now includes HA, CLI.

basis is to refactor file-based support to use a common PersistenceObjectStore interface backed by either filesystem or jclouds blobstore (running w softlayer only so far, but using jclouds).

to run integration tests against SL, set up a named location such as the following:

    brooklyn.location.named.softlayer-objectstore-amsterdam-1=jclouds:swift:https://ams01.objectstorage.softlayer.net/auth/v1.0
    brooklyn.location.named.softlayer-objectstore-amsterdam-1.identity=IBMOS1234:yourname
    brooklyn.location.named.softlayer-objectstore-amsterdam-1.credential=....

i think this is the right way, people who want to run integration tests simply have to set up a location with this name.  `brooklyn.properties` is explicitly read for these tests.  so add something like:

    /**
     * Integration tests as written require a location defined as follows:
     * 
     * <code>
     * brooklyn.location.named.brooklyn-jclouds-objstore-test-1==jclouds:swift:https://ams01.objectstorage.softlayer.net/auth/v1.0
     * brooklyn.location.named.brooklyn-jclouds-objstore-test-1.identity=IBMOS1234-5:yourname
     * brooklyn.location.named.brooklyn-jclouds-objstore-test-1.credential=0123abcd.......
     * </code>
     */
    public static final String PERSIST_TO_OBJECT_STORE_FOR_TEST_SPEC = "named:brooklyn-jclouds-objstore-test-1";

(i've added the above to the code)

/cc @grkvlt can you set this up on our integration test servers?