mke2fs: don't ask the proceed question using a regular file

mke2fs: don't ask the proceed question using a regular file

Very often people are creating file systems using regular files, so we
shouldn't ask the user to confirm using the proceed question.
Otherwise it encourages users to use the -F flag, which is a bad
thing.

We do need to continue to check if the external journal device is a
block device.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>