supports legacy bash-style (lower-hyphen) format for key settings

e.g. private-key-file instead of privateKeyFile.

re-instates needed backwards compatibility following recent locations overhaul.

we should ALSO support for locations:

(1) declaring earlier in the extenstions hierarchy (e.g. named:abiquo extending jclouds:abiquo, with a brooklyn.jclouds.abiquo.key=value, you end up with key=value in the location -- this may be working but make sure we have a test)

* declaring higher in the dot-namespacing hierarchy, for selected keys (such as those defined as statics, or perhaps just those in LocationConfigKeys), including:

(2) brooklyn.privateKeyFile

(3) brooklyn.jclouds.privateKeyFile 

(4) brooklyn.jclouds.private-key-file

(5) brooklyn.private-key-file

Of these (4) and (5) should be deprecated.  (And if we didn't previously support (5) we don't need to add it.)  But (2) and (3) I think are important -- certainly (3) is needed for backwards compatibility but I also think it's a good thing, i.e. to be able to specify a private key file to use across the board.