[ros] Add mavros_msgs to build dependencies

[jsharpe]

If mavros is being built in the same catkin workspace then airsim_ros_pkgs needs to depend upon mavros_msgs for the packages to be built in the correct order.

[madratman]

This doesn't really fix the issue.
sudo apt-get install ros-melodic-mavros* can be added to the docs

[madratman]

But ok, if some one is compiling it from source, we should have that in list of deps.
Wouldn't it also be a runtime dep?

[jsharpe]

But ok, if some one is compiling it from source, we should have that in list of deps.
Wouldn't it also be a runtime dep?

RIght - it should just be a <depend> node, also a number of the other msgs dependencies could be converted to just a <depend> to remove duplication. Also now I look at it why is it depending upon message_generation at exec time? Seems like there is some clean up to be done in the packages.xml file

[madratman]

ah yes, it should be

<build_depend>message_generation</build_depend> 
<exec_depend>message_runtime</exec_depend>

Yeah, I agree the <depend> tag can half the number of lines for sure, as it's kinda like a catch-all. Please feel free to add that on to this PR. If not, I can do that, and merge this one. Lemme know.