Using a default external provider in examples ?

[Alex Heneveld <al...@cloudsoftcorp.com>]

Hi All-

I've had a couple exchanges where people are put off by passwords shown 
in plain text in our demos.  It's all well and good explaining it's for 
demo but if we say "of course you should use an external provider" then 
our examples do also.

In order not to require additional setup of this by the user, I've added 
a default external provider for review [1].  You can use this as follows:

     $brooklyn:external("brooklyn-demo-sample", "hidden-brooklyn-password")

I've added documentation explaining this at [2].  I'll update our 
examples in the examples repo and the docs shortly and open new PRs.

If anyone thinks this isn't the way to go, just say.  If no one speaks 
up then could someone who really likes this review and merge the various 
PRs?  (Give 24h for people to comment and me to finish the rest of the 
items.)

Best
Alex

PRs are:

[1] https://github.com/apache/brooklyn-server/pull/812
[2] https://github.com/apache/brooklyn-docs/pull/209