jenkins only uses the ROS repository, not the gazebo repository, so it can't find the ros-indigo-gazebo5-* packages.

The ros-indigo-gazebo5-* packages have the same ROS package names as the ros-indigo-gazebo-* packages, so they would collide if they were both installed at the same time.

At the time that ROS Indigo was released, Gazebo 2 was the current version of gazebo, and so that version was chosen as the standard version for ROS Indigo. Since Gazebo does not make their ROS packages installable side-by-side for different versions, the later versions of the gazebo-ros packages are not installable by default.