Fix reusable node regex for proposal node.

The regex that set reusable node on proposal node jobs did not match the
names of the requirements proposal jobs. Edit the regex so that it
matches.

Regex should match: propose-requirements-updates
but would only match .*-propose-requirements-updates.

Change-Id: I5445bf416c407b0deb6229c3e022e69af93e4dea