Add keepWorkspace option

[SleepWalker]

This is a last portion of improvements to finally solve #207

I've added new config option, which will disable workspace deletion step and also documented two possible ways of configuring workspace path

[SleepWalker]

@neoziro can you please take a look?

[gregberge]

Hello @SleepWalker, it looks good but could you please try to make tests pass?

[SleepWalker]

oh my, haven't noticed that :) It's now should be green (I hope)

[SleepWalker]

@neoziro there is an issue because both shallowClone and workspace props set deploy config:

According to the logic before my PR, that workspace from config will be silently overridden with tmp dir, if shallowClone: true. I've removed that logic in my PR and if workspace config is set, than it has the biggest priority.

I'll revert this change and will log the warning, that workspace from config was overridden with tmp dir because of shallowClone option. This will be more clear to use and won't be a breaking change for existing users (and won't break tests too)

[gregberge]

Thanks!