convert breach migration plugin to proper gem and fix name

Change-Id: Ie26495b5ea3e09f31b6b80d643679fe94ca9816b
Reviewed-on: https://gerrit.instructure.com/29455
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Stephan Hagemann <stephan@pivotallabs.com>
Product-Review: Stephan Hagemann <stephan@pivotallabs.com>
QA-Review: Stephan Hagemann <stephan@pivotallabs.com>