[Travis] Switch to Ubuntu 18.04 Bionic and add workaround for urdf_parser_py regression

[traversaro]

See robotology/simmechanics-to-urdf#36 and ros/urdf_parser_py#47 for more info on the regression.
See https://docs.travis-ci.com/user/reference/bionic/ for the Ubuntu 18.04 Bionic.

If this is successful, hopefully it would simplify reproducing the Travis failure in https://travis-ci.org/robotology/icub-model-generator/builds/570949195 mentioned in #113 (comment) .

[prashanthr05]

Any update on this?

[traversaro]

Let's see.

The latest error is:

/usr/bin/ld: cannot find -lconsole_bridge::console_bridge

collect2: error: ld returned 1 exit status

This should have been fixed by f2a4ce2, but it did not. Let's see why.

[traversaro]

To move the CI system closer to my system (where everything was working fine), in 1fafc9d I switched to use the Ubuntu packages for orocos_kdl, console_bridge, urdfdom_headers and urdfdom.

[traversaro]

The latest failure is much more interesting, for dh-generated models we have this problem:

icub-model-test error:torso_pitch got direction of x 0 y 1 z 6.12323e-17 instead of expected x 0 y -1 z 0

Probably something changed in some of the dependency related to dh-models generation: iDynTree, YARP or icub-main .

[traversaro]

After a quick local check, I could not got the test to pass even with the YARP/ICUB/iDynTree checkouts from robotology/icub-models@b69b989 . To be more methodic and to avoid problems related to system dependencies between xenial and bionic, we will first try to get the tests to pass in Xenial (on Travis) in #119 .

[traversaro]

Superseded by #119 .