2.2 bundle include fixes

[howbazaar]

This branch addresses two bugs found in processing bundles, and one that hadn't yet been found.

When the local processing of the include directives came across a machine without a machineSpec, which would happen if nothing was specified, it paniced.

Also, when a bundle was processed as a directory, not a file, then the bundleDir was empty rather than the directory specified. This meant that the bundle was considered a charmstore bundle, not a local bundle, so Verify was called on the bundle rather than VerifyLocal. This would have meant that local resources would fail validation.

QA steps

# Have a local bundle directory (needs bundle.yaml and README.md)
# Make sure there is a machine defined with nothing extra.
juju deploy .

Bug reference

pad.lv/1716462 and pad.lv/1716482

[howbazaar]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://ci.jujucharms.com/job/github-merge-juju