Option for skipping checkout of existing repositories

[leorochael]

Checking out lots of addon repositories (or even the huge odoo repo itself) can take a long time, and sometimes we just want to re-run buildout for some other purpose. Examples include:

• rebuilding odoo.cfg
• adding another python package in eggs =
• temporarily working on an addon in a branch that is different than the one specified in buildout.cfg but wanting to re-run buildout for one of the above reasons.

Some of these can be achieved by using the buildout:offline setting (i.e. by running bin/buildout -o) but others can't. And even the offline run can be faster by skipping the checkouts.

This PR adds an option for skipping the checkout of a repo if the target already exists.

It's mostly to be used from the buildout command line, like:

 bin/buildout odoo:skip-checkout=true

[petrus-v]

Thanks for this PR, reading your description I wonder why you are not using buildout offline option?

bin/buildout -c buildout.cfg -o

[leorochael]

Thanks for this PR, reading your description I wonder why you are not using buildout offline option?

I am, for some of the cases. But there are some other cases where I'd like to skip checkout even in non-offline mode. I've clarified some more use cases in the PR description.

[coveralls]

Coverage increased (+0.07%) to 86.516% when pulling 78f8cfb on leorochael:leorochael-skip-checkout into f14b801 on anybox:master.

[coveralls]

Coverage increased (+0.07%) to 86.516% when pulling 60c1b6e on leorochael:leorochael-skip-checkout into f14b801 on anybox:master.