init_working_dir should reuse cloned git repos for efficiency

[noisecapella]

Currently init_working_dir will git clone each time it is used, which is frequently. Instead, we should have some known directory (/tmp/doof/repo-name-here for example) and:

• on the first call of init_working_dir clone into that directory
• on any future calls, clear away any changes in the git repo including commits made and fetch new changes