We're adding the ability to have devstack plugins, which should be
much more free to require new things not in global requirements. Our
old thinking of locking down all the requirements doesn't really work
in a plugin model.
Instead, if the project is in projects.txt, continue with the old
behavior. If it is not, do a soft update (update all the requirements
we know about, leave the ones we don't). This was previously the SOFT
requirements update mode, but now it will just be the default.
Change-Id: Ic0c6e01a6d7613d712ac9e7e4a378cc3a8ce75e6
7af8a1b9b3