Add failing local repository tests

[colearendt]

Add packages, repo, and tests for local repository behavior. Both tests fail per discussion in #153

• breakfastcereal project is using cereal package 1.0.0, but the repo testrepo has moved on to version 2.0.0. The Repository: testrepo field is set, but packrat still fails to pull sources for 1.0.0 (even though sources for that version are available in the repository).
  One note on this one... packrat.lock picked up a dependency on packrat-4.8.1, which is probably bad for go-forward testing here. Not sure how to resolve that issue. Making this test pass would be hugely helpful to the maintenance of external packages not yet on (or not relevant for) github or CRAN, so projects can grab sources for old versions of the package without issue. i.e. a drat repo

• breakfastyogurt project is using the yogurt package 1.0.0, but the Repository: testrepo field is not set in the package. Packrat fails to load the package, even though the repository is defined in getOption('repos'), so finding the package yogurt should be do-able. Per discussion on Error in snapshot() with packages installed from external source #153 , the preferred behavior seems to be loading the package even if Repository: testrepo is not set. See comment from 10/4/2016 2:04am (EST)

[colearendt]

NOTE: Need to update the test for breakfastcereal. Using drat::archivePackages allows things to work perfectly fine!