eigenpyConfig.cmake: find absolute library paths for all required libs

[rhaschke]

As cmake expects absolute library paths, while pkgconfig provides lib names only (together with
LIBRARY_DIRS), one needs to transform names to full library paths.

This fixes 7854c0f / #101. Without this fix, the MoveIt catkin build still fails with:

Errors     << moveit_ros_planning_interface:make /vol/sandbox/ros/logs/moveit_ros_planning_interface/build.make.000.log
/usr/bin/ld: cannot find -leigenpy
collect2: error: ld returned 1 exit status

[wxmerkt]

Thank you for the fix @rhaschke. I think this is neater than #108, which also works in compiling MoveIt.

[rhaschke]

Yeah, using link_directories is "bad" style, because it might introduce unintended side effects.

[rhaschke]

@wxmerkt, maybe you want to close #108 in favor of this PR?

[jcarpent]

@rhaschke Thanks for the fix. I will merge it.

[rhaschke]

Thanks for this quick merge!
@wxmerkt, can you please prepare a new (Kinetic and Melodic) release to fix the issues on the ROS build farm? Thanks.

[jcarpent]

I will handle it ;)

[wxmerkt]

Kinetic: ros/rosdistro#22934
Melodic: ros/rosdistro#22935