[naoqieus/cross] use $ROS_DISTRO instead of melodic when installing pepper_meshes to allow us to use ROS noetic for build cross environment

[kochigami]

Related commit:
kochigami@1a0cfe0
#1583

When I used ubuntu 20.04 + ROS noetic PC, ./build_user.sh of pepper cross failed.
That is because this script tries to copy /opt/ros/melodic/share/pepper_meshes/meshes/ forcefully.

kochigami@kochigami-pc:~/catkin_ws/src/jsk_robot/jsk_naoqi_robot/cross$ ./build_user.sh

.......

+ vcs import i386_User/src
.........
=== i386_User/src/app_manager (git) ===
Cloning into '.'...
=== i386_User/src/nao_interaction (git) ===
Cloning into '.'...
=== i386_User/src/nao_robot (git) ===
Cloning into '.'...
=== i386_User/src/naoqi_bridge (git) ===
Cloning into '.'...
=== i386_User/src/naoqi_bridge_msgs (git) ===
Cloning into '.'...
=== i386_User/src/naoqi_dashboard (git) ===
Cloning into '.'...
=== i386_User/src/naoqi_driver (git) ===
Cloning into '.'...
=== i386_User/src/pepper_meshes (git) ===
Cloning into '.'...
=== i386_User/src/pepper_robot (git) ===
Cloning into '.'...
+ '[' '!' -e i386_User/src/pepper_meshes/meshes ']'
+ '[' '!' -e /opt/ros/melodic/share/pepper_meshes/meshes/ ']'
+ set +x
ERROR: You need /opt/ros/melodic/share/pepper_meshes/meshes/ 

Therefore, I changed melodic to $ROS_DISTRO in https://github.com/jsk-ros-pkg/jsk_robot/blob/master/jsk_naoqi_robot/cross/build_user.sh#L45-L52.
When I checked cross/i386_User/src/pepper_meshes/package.xml, version 0.2.5 was installed.