provider/azure: make boilerplate <> usage consistent

Remove <> from boilerplate values for consistency's
sake, to reduce confusion about what needs replacing.
This matches the docs.

Fixes https://bugs.launchpad.net/juju-core/+bug/1381289
Allow env-set to handle deprecated attributes
Tweak test
Merge pull request #1015 from axw/lp1381289-azure-boilerplate-consistency

provider/azure: make boilerplate <> usage consistent

Remove <> from boilerplate values for consistency's
sake, to reduce confusion about what needs replacing.
This matches the docs.

Fixes https://bugs.launchpad.net/juju-core/+bug/1381289
Make add-metric test independent of map ordering.
Allow empty values in juju set-env.
Merge pull request #1020 from tasdomas/fix-1388073

Fix 1388073 and the worker/uniter/jujuc test failure in 1387936

Command line parameters for juju set-env were being parsed incorrectly, not allowing empty values ('key=') - that was fixed and a test added to avoid future regressions.

Tests for worker/uniter/jujuc were failing on PPC due to reliance on map ordering, which is not guaranteed. Fixed.
Merge pull request #1016 from wallyworld/deprecated-set-env

Allow env-set to handle deprecated attributes

Fixes: https://bugs.launchpad.net/bugs/1387953

Customers will not be hitting this issue but the CI scripts do because they set tools-metadata-url during the course of CI testing.

When set-env is used, you can now pass in deprecated attributes and they will be converted to the new values. The code used to initially parse env config is shared.

As a drive by, convert some more config string literals to constants.
Write metadata for ppc64; do not write product metadata if it has not changed
Small tweak
Refactor metadataUnchanged to be clearer
Explicitly pass in the streams for which to write metadata
Merge pull request #1021 from wallyworld/simplestreams-ppc64

Write metadata for ppc64; do not write product metadata if it has not changed

Fixes: https://bugs.launchpad.net/juju-core/+bug/1388493

This PR does 2 things:

1. If tools for ppc64el are found, metadata is also generated for ppc64 so that older versions of Juju which look for ppc64 can find tools.

2. When writing simplestreams product metadata for tools, if the generated metadata is the same as what's there, do not overwrite the file.