simplify request handling in Power Settings widget

This brings it closer in line with the other widgets, and simplifies
a bunch of things by using .button('loading').

The key point is that we can't just listen for the System 'sync' and
'error' events since they are triggered by *any* requests relating to
the System model, including requests made by other widgets.

Bug: 1161373
Change-Id: I4bf5875b7f048296b2d2e2e79120c364152f29f3
make beaker-job.rng a Sphinx download

This keeps it versioned with the Beaker branch where it came from, and
also lets us avoid the copying step in the web site build.

One day in the distant glorious future, we will have a Sphinx plugin to
convert the schema into some human-readable form also...

Bug: 980340
Change-Id: Ie0f6d7784c4301dc220df281767c015aa769969b
swapsize ksmeta should trigger custom partitioning

Also removed --recommended from the part command when a size is given,
because that was causing Anaconda to just ignore the size anyway.

Bug: 854229
Change-Id: Ibf44e75aa893171eb97151fee8af8a2e46be3e9b
beaker-init: split db population step out, always run it

This actually changes it back to match the pre-19.0 behaviour: the
schema is first created (or upgraded) if necessary, and then any
skeleton values are populated if necessary.

With this change the logic for setting up new admin users, or converting
existing users into admins, will always take effect no matter whether
you are starting from an empty schema, an outdated schema, or an
up-to-date schema.

Bug: 745560
Change-Id: I997a851d620ee6d391b942c32b3e1ea402006361
Merge branch 'release-19' into develop