[exotica_python] Fail nicely when pip installed trimesh isnt available

pip keys cannot be used for release on the buildfarm, hence we fail with
a warning when trimesh cannot be found. Also comments the key from
package.xml to make release builds possible.

exotica_python/package.xml

@@ -20,6 +20,10 @@
  <exec_depend condition="$ROS_PYTHON_VERSION == 3">python3-pyassimp</exec_depend>
  <exec_depend condition="$ROS_PYTHON_VERSION == 3">python3-tk</exec_depend>
  <exec_depend condition="$ROS_PYTHON_VERSION == 3">python3-rospkg</exec_depend>
- <test_depend condition="$ROS_PYTHON_VERSION == 2">python-trimesh-pip</test_depend>
- <test_depend condition="$ROS_PYTHON_VERSION == 3">python3-trimesh-pip</test_depend>
+ <!--
+ pip keys cannot be used for releases on the buildfarm cf. 
+ https://github.com/ros/rosdistro/pull/39892#issuecomment-1985640859
+ -->
+ <!-- <test_depend condition="$ROS_PYTHON_VERSION == 2">python-trimesh-pip</test_depend>
+ <test_depend condition="$ROS_PYTHON_VERSION == 3">python3-trimesh-pip</test_depend> -->
 </package>

exotica_python/test/test_mesh.py

@@ -1,7 +1,12 @@
 import unittest
 
 import pyexotica as exo
-import trimesh
+try:
+ import trimesh
+except ImportError:
+ import warnings
+ warnings.warn("trimesh not found, skipping test")
+ exit()
 
 def validate_mesh(mesh):
  print(mesh, mesh.vertex_count, mesh.triangle_count)