Have master-side SVN steps respect the timeout when removing files and directories.

Teach CompositeStepMixin.runRmdir to respect any timeout from the step.

Fixes ticket:3055.
Move source steps over to the CompositeStepMixin.runRmdir now that it
uses the appropriate timeout.

This addresses problems similar to issue 3055 in other source control types.
Merge pull request #1369 from bdash/fix-3055

Have master-side steps respect the timeout when removing files and directories