Upgrade Boost include directories for ur_kinematics

[stefanscherzinger]

Branch: calibration_devel
Use case: The issue came up here.

Problem statement:

The ur_kinematics package seems to use Boost includes via include_directories(SYSTEM ${Boost_INCLUDE_DIR}), which is a cache entry.

I'm not sure, though, why and how ur_kinematics would drop the own generation of such cache entries in that case, despite the package's

find_package(Boost REQUIRED COMPONENTS system)

Possible solution:
Use the result variable instead, as recommended here.

include_directories(SYSTEM ${Boost_INCLUDE_DIRS})

[fmauch]

Let me come back to this later...

[fmauch]

This issue should be migrated to the upstream repo. As ur_kinematics needs some attention, anyway this might be a relevant point to consider.

[fmauch]

Closing in favor of ros-industrial#603