Allow the Singularity wrapper to ensure unicity of bind mounts
Dave pointed out to me that older 3.x versions of Singularity were failing it the same destination is mounted twice (this is just a warning in 2.x and 3.1.1).
An option in the checks for the bind mounts could ensure that the same destination is not used twice.
Simple behavior consistent w/ Singularity is to use the first one and discard w/ a warning the following mounts on that destination
Evaluate the possibility to have a uniqueness selection where following definitions override the previous one. The main question is to define a consistent behavior between Factory, Frontend, and defaults. Which one sets the values, which ones can be overridden?