Minor fixes for the --skip-keys option.
Minor fixes for the --skip-keys option.

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