detect already installed packages on webpi source

[brettporter]

This change ensures that packages using source => webpi do not get marked as created on every Puppet execution, by detecting they are already installed.

The parsing is a little crude but should work. I've submitted chocolatey-archive/chocolatey#521 to avoid the need to exclude Available Products at some future time.

Note that this doesn't list the packages in self.instances. I'm not sure what the impact of that is for the provider. The only way I could think of addressing that is to split webpi into a separate provider, where every operation uses -source webpi. This might make sense as a next step regardless, so that it can have correct capabilities (e.g., latest also doesn't make sense on webpi, and it is not versionable). Would that be a change you'd consider?

[ferventcoder]

This is probably okay performance-wise. Granted it would be nice to cache this the first time this was called so it's only called once.

[ferventcoder]

@brettporter Can you start looking at 0.9.10 (it's in alpha) and seeing how this applies again?

[ferventcoder]

This depends on chocolatey/choco#14 (which is part of 0.9.10)

[brettporter]

Sorry @ferventcoder - I stopped working on the project that needed this, and I'm not setup to try it out again.

[ferventcoder]

Closing this for now. If at some point in the future you want to pick this up (which now it may not be necessary as choco may be able to detect something is already installed through webpi), please feel free to file a new PR. It may be better to ensure this functionality in Chocolatey itself though instead of in the provider. Thanks!