Cache omnibus download, expose config options

[tknerr]

I messed up history in #71. This one is rebased on master.

Fixes #68

Instead of using an env var the config option config.omnibus.cache_packages is introduced. By default it is true, so it can be turned off if you don't want the caching behaviour.

Additionally the config.omnibus.install_url option has been exposed. The $OMNIBUS_INSTALL_URL is still considered, but has lower precedence than the config option.

cache_packages

Caching kicks in only iff:

• cache_packages is truthy
• the vagrant-cachier plugin is present
• the vagrant-cachier plugin has config.cachier.auto_detect enabled (which is the default)

If caching kicks in -d /tmp/vagrant-cache/vagrant_omnibus will be passed to install.sh so this will be the location on the guest to which a) the omnibus package will be downloaded and b) which will be cached by vagrant-cachier.

The config option is truthy. Currently we default to true, but if more caching strategies would be implemented in the future it could be :cachier, :something_else or :whatever as well. Only false or nil will disable the caching behaviour.

install_script

The precedence is now:

1. try config.omnibus.install_url if set
2. try ENV['OMNIBUS_INSTALL_URL'] if set
3. use default url for install(.sh|.msi)

There is some basic validation in place at install time (didn't change anything here). You can pass in for example:

config.omnibus.install_url = 'http://some_path.com/install.sh'
config.omnibus.install_url = 'http://some_path.com/install.msi'
config.omnibus.install_url = '/some/path/on/the/host'

[tknerr]

@schisamo build fails due to a bug in rubocop 0.19.1 that is already fixed in master (see rubocop/rubocop#892). I have now pinned rubocop to 0.18.1 in the gemspec to unblock the travis build here.

[schisamo]

Thanks for the PR! Hoping to have some time to get this integrated next week.

[ivanoats]

excited for this, especially because I'm commenting from hotel wifi while waiting for omnibus 👍

[fgrehm]

👍 great work 🎆

[drpebcak]

Any idea when there is going to be a release that includes this? I'm stoked to be able to use this!

[woodsae]

👍 Can't wait for this!

[gwaldo]

Likewise, I am excited for this to be released! (I just read through a couple github comment threads on this issue/feature.)

[esciara]

Yes! When is this going to be released?! Looking forward to have my tests speeding up as a result. :)

[cromulus]

👍 Awesome work Humans of Github! My development workflow and sanity thanks you.

[schisamo]

THANK YOU! I think that was the last sane version of Rubocop! 😄