Support more options for singularity run and singularity exec (--pwd)

[namheegordonkim]

Client.run() and Client.exec() only support a subset of the options available. From the API:

variable	example	default	description
bind	add one or more –bind as a list or string	None	one or more bind mounts
contain	add the –contain flag	False	contain the environment and mounts
writable	singularity build –writable	False	build a writable image

I'm using a Docker container that requires working directory to be set, which can be done using the --pwd option. This is not yet supported it seems.

[vsoch]

hey @namheegordonkim if you would like this for the singularity command line client, the repo you want to post to is -> https://github.com/singularityhub/singularity-cli. Thanks!

[vsoch]

Actually if you just want to confirm this is the case, I can transfer the issue for you!