Add command to upgrade all packages

[bfirsh]

Iterate through all the packages and run docker pull on them:

$ whalebrew upgrade

Ref #3

[nithin-bose]

Could there be a better way than to docker pull all installed images in a loop??

[nithin-bose]

Updates might require the package file to be regenerated. You know if the labels have changed or something?
Thoughts??

[bfirsh]

@nithin-bose Yeah, that's an issue. Particularly if the user has edited the package file.

Perhaps the package file could be blank by default (except for image), then all the options could be figured out at runtime by inspecting the image. Then, the package file is only user-editable stuff.

[nithin-bose]

Hmm that makes sense but would that add a significant delay to command execution??

Also existing users might never get the updated label values in the image, unless they reinstall the app.

[bfirsh]

An image inspect is extremely fast. (On the order of 10ms with Docker for Mac IIRC, but we could benchmark it.)

Backwards compatibility is certainly an issue. Perhaps Whalebrew could remove labels which match the value in the image to convert them to this new format. To make it a one-off, we could add a version: 1 key, then that'd give us an opportunity to make changes like this in the future.

[nithin-bose]

How about we use image inspect as default values?? That is when a command is run the following steps happen:

1. Read the package file to get the image name (only mandatory field in the pkg file)
2. Inspect the image to get labels set
3. Override the values taken from image with that defined in the package file. If something is not defined in the pkg file, the value from image inspect would be used. This way, a user would be able to override any value by editing the pkg file and yet any new labels introduced in a later version of the image would still be applied
4. Run the container with the values after step 3

If we use the the above method, we should be able to support current installs as well without a version number. The only corner case for existing installs is if the value of a label has changed or if a label has been removed in a newer version, in which case the user will have to reinstall the app.

Even with a version number, its not trivial to update the version of a pkg file of an installed app and is probably easier to just reinstall the app.

Thoughts??