mke2fs: Use a fs_type of 'journal' when creating an external journal

mke2fs: Use a fs_type of 'journal' when creating an external journal

If creating a an external journal via "mke2fs -O journal_dev",
override the fs_type list (i.e., "ext2", "small"), and replace it with
an fs_type list of "journal".  This will prevent external journals
smaller than 512MB from being created with a block size of 1k, which
is not very useful and leads to much confusion.

Addresses-Debian-Bug: #488663

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