Alow multiple invocations of --container-mounts in SBATCH header

[cponder]

The list of container-mounts has a way of getting long; there are ways to build the list more legibly on the command-line, but in the #SBATCH header we can't compose variables. I'd like to be able to split the list for legibility, like

#SBATCH --container-mounts ....
#SBATCH --container-mounts ...
#SBATCH --container-mounts ...

[cponder]

(though the singular form "container-mount" would be more appropriate than the plural "container-mounts"...)