The doctors it was built for are not all here yet. The building is open. The roster is not. Dignity Health’s new Sierra Pacific Regional Cancer Center in Redding began seeing patients at the end of August, but Mercy’s own leaders say the $70 million campus is still short of the oncologists it was built for — and the help-wanted ads are still up, even with a five-year guarantee of $770,000 a year. REDDING — Dignity Health spent years, a riverfront site, and $70 million to put