create test to expose issue #146 regression
debian: do not clear debian folder on templating

This changes the default behavior when expanding
the debian folder templates to preserve the
debian folder rather than clear it.

In interactive mode it already asked, but most
users do not run this command interactively.

The old behavior can be done by setting the
BLOOM_CLEAR_DEBIAN_ON_GENERATION environment var.
Merge pull request #322 from ros-infrastructure/issue_146_regression

issue #146 regression, files in debian folder are lost