Fix ElectroHydraulic crash

[chapulina]

A little crash was introduced in #3. Try for example:

ros2 launch buoy_gazebo mbari_wec.launch.py

Then press play, and the simulation crashes.

Originally, the rand() function was used, but that resulted in this warning:

Consider using rand_r(...) instead of rand(...) for improved thread safety.  [runtime/threadsafe_fn] [2]

The proposed fix here is to use a fixed a seed when calling rand_r. This should make the simulation more deterministic, which is usually desirable. But if we really want a different value each time the simulation is run, we could seed it with the current time.

[quarkytale]

Hmm this shouldn't have creeped in, the fix for it is already merged in this commit