Alpaka: Boost 1.69.0 beta 1

[ax3l]

Boost 1.69.0 beta 1 is released, shall we give it a try before the main release? :)

[BenjaminW3]

I created a branch to test it. Let's see.

[BenjaminW3]

boost.test can not be found. No time at the moment to look into this: https://travis-ci.org/BenjaminW3/alpaka/builds/462096169

[ax3l]

Hm, they improved the install somehow which probably breaks the CMake FindBoost module.
https://www.boost.org/doc/libs/1_69_0_beta1/libs/test/doc/html/boost_test/change_log.html

[BenjaminW3]

Thanks for the hint! I will try out the newly documented header-only-mode. Maybe this solves our problem and also removes the necessity to build and link the lib.

[BenjaminW3]

The build is getting green now.

[BenjaminW3]

Tested since #717