use dev-requirements for global sync

This allows us to pass through an exact line from
dev-requirements.txt as valid, if it's not exactly valid we'll
revert to the base requirement. This is needed so that projects
can keep development requirements in their tree.

Redo an if statement to make E125 happy....

Change-Id: I50a1292c321b7092ca1c7aeee5068f0828ece7b0