Allow empty lines in neuro run --env-file

[atemate]

I want the env-file to allow empty lines because it's a real use-case to have empty lines:

1. separator
2. lack of trailing emptyline is hard to maintain in an automated workflow.

[ay@archlinux ~]$ cat env
key=val
val2

[ay@archlinux ~]$ neuro run -s cpu-small -n test-env --env-file=env ubuntu "true"
ERROR: Illegal argument(s) ({'container': DataError({'env': DataError({'': DataError({'key': DataError(blank value is not allowed)})})})})
[ay@archlinux ~]$ vim env