Fix bug in rosdistro helper
Fix bug in rosdistro helper

When hot-switching index url, need to flush the cache

spaghetti-/rosdep,georgepar/rosdep,allenh1/rosdep,sorki/rosdep,wkentaro/rosdep,sorki/rosdep,alessandro-aglietti/rosdep,aymanim/rosdep,allenh1/rosdep,wkentaro/rosdep,aymanim/rosdep,ros-infrastructure/rosdep,georgepar/rosdep,spaghetti-/rosdep,alessandro-aglietti/rosdep,ros-infrastructure/rosdep