Skip git run on target and fill revision correctly

Issue description: capistrano 3 tries to run git on target for git:check and git:create_release (which fails since there may be no access to local repo from target system). Also revision version is not passed to target system.
Root cause: Without Rake::Task.clear new task definition is not replacing, but appending new functionality.
Solution: Added clear of git:check, git:create_release and git:set_revision. Fill current_revision capistrano variable after cloning locally