Update dependency rules for new arch and series

Update dependency rules for new arch and series

This branch corrects recent dependency changes made by myself. Juju CI
failed the unit test runs for trusty+arm64 and precise+amd64. I am
both incompetent and naieve. We cannot query apt-cache until after the
PPAs are added (for old series) and the cache updated. The golang
package is available for arm64, but it doesn't work (why is it there?).

The go compiler is now selected by matching the uname arch to a list
of arch that golang-go really supports. This rule is easier to read.

The rule to select the juju-db is evaluated at the moment apt-get
install is called. I was able to eliminate the regex after
verifying that apt-cache reports the matching packages in the same
order they were passed. It returns a vetted and prioritise list. We
care about the first line, and only need the name field.

https://code.launchpad.net/~sinzui/juju-core/better-arch-series-deps/+merge/209736

(do not edit description out of merge proposal)

[curtis, 2014-03-06 17:29:47]

Please take a look.

[natefinch, 2014-03-06 17:49:05]

On 2014/03/06 17:29:47, curtis wrote:
> Please take a look.

LGTM