e2image: If there is an error while writing a block, call exit(1)

e2image: If there is an error while writing a block, call exit(1)

If the disk fills while e2image is writing its output file, it will
spew a large number of error messages instead of exiting with a
non-zero status code after the first failure.

Addresses-Sourceforge-Feature-Request: #606508

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