modify plugin path to match rmf_simulation install (open-rmf#108)

Signed-off-by: Marco A. Gutierrez <marco@openrobotics.org>

rmf_demos_gz/launch/simulation.launch.xml

@@ -9,7 +9,7 @@
   <let name="world_path" value="$(find-pkg-share $(var map_package))/maps/$(var map_name)/$(var map_name).world" />
   <let name="model_path" value="$(find-pkg-share $(var map_package))/maps/$(var map_name)/models:$(find-pkg-share rmf_demos_assets)/models:/usr/share/gazebo-$(var gazebo_version)/models" />
   <let name="resource_path" value="$(find-pkg-share rmf_demos_assets):/usr/share/gazebo-$(var gazebo_version)" />
-  <let name="plugin_path" value="$(find-pkg-prefix rmf_robot_sim_gazebo_plugins)/lib:$(find-pkg-prefix rmf_building_sim_gazebo_plugins)/lib:/usr/share/gazebo-$(var gazebo_version)" />
+  <let name="plugin_path" value="$(find-pkg-prefix rmf_robot_sim_gazebo_plugins)/lib/rmf_robot_sim_gazebo_plugins:$(find-pkg-prefix rmf_building_sim_gazebo_plugins)/lib/rmf_building_sim_gazebo_plugins:/usr/share/gazebo-$(var gazebo_version)" />
 
   <!-- Use crowd sim if `use_crowdsim` is true-->
   <let name="menge_resource_path" if="$(var use_crowdsim)" value="$(find-pkg-share $(var map_package))/maps/$(var map_name)/config_resource"/>

rmf_demos_ign/launch/simulation.launch.xml

@@ -8,7 +8,7 @@
 
   <let name="world_path" value="$(find-pkg-share $(var map_package))/maps/$(var map_name)_ign/$(var map_name).world" />
   <let name="model_path" value="$(find-pkg-share $(var map_package))/maps/$(var map_name)/models:$(find-pkg-share $(var map_package))/maps/$(var map_name)_ign/models:$(find-pkg-share rmf_demos_assets)/models:$(env HOME)/.gazebo/models" />
-  <let name="plugin_path" value="$(find-pkg-prefix rmf_robot_sim_ignition_plugins)/lib:$(find-pkg-prefix rmf_building_sim_ignition_plugins)/lib" />
+  <let name="plugin_path" value="$(find-pkg-prefix rmf_robot_sim_ignition_plugins)/lib/rmf_robot_sim_ignition_plugins:$(find-pkg-prefix rmf_building_sim_ignition_plugins)/lib/rmf_building_sim_ignition_plugins" />
   <!-- Use TPE if` use_tpe` is set to true-->
   <!-- TODO use the variable below and remove code duplication (second ign gazebo command) when substitution in XML with ignition gazebo works -->
   <let name="tpe_engine" value="\-\-physics-engine ignition-physics-tpe-plugin" />