Fix: allow directories for --device and in-container path (fix #2985)

[apostasie]

Fix #2985

Patch is much simpler than I thought, as containerd provides ready-made helpers for that.

Incidentally, this patch also allows for in-container path for devices.

Local testing:

apo@oliphant:~ $ sudo ./nerdctl run -ti --device /dev/snd:/somethingelse debian ls -lA /somethingelse
total 0
crw-rw---- 1 root audio 116,  3 May 11 05:09 controlC0
crw-rw---- 1 root audio 116,  5 May 11 05:09 controlC1
crw-rw---- 1 root audio 116,  2 May 11 05:09 pcmC0D0p
crw-rw---- 1 root audio 116,  4 May 11 05:09 pcmC1D0p
crw-rw---- 1 root audio 116,  1 May 11 05:09 seq
crw-rw---- 1 root audio 116, 33 May 11 05:09 timer

[apostasie]

@AkihiroSuda can you take a look?

Thanks.

[AkihiroSuda]

Thanks