luks_device: Add disk image supports

[ba0f3]

LUKS is able to create/open a disk image/ file, so please add disk image supports by add S_ISREG checking here

community.crypto/plugins/modules/luks_device.py

Line 887 in d0d99c3

if not stat.S_ISBLK(mode) and not stat.S_ISCHR(mode):

[felixfontein]

This might be more tricky, since "device" is built into the module in some more places (see also the usage of lsblk).

[sietsevanderbom]

I think I was looking for the same feature. I saw this:
http://freesoftwaremagazine.com/articles/create_encrypted_disk_image_gnulinux/

Which makes a luks virtual volume from an .iso file. Tried to do this with ansible using luks_device, but only device is accepted.

[felixfontein]

One useful bit needed to implement this is losetup -j /path/to/file --output name. (I would prefer to use --json instead of parsing the text output, but that's not supported on CentOS 6 and 7, for example; it was only added in June 2015 in util-linux/util-linux@4827093.)