tests: fix i_e2image so it works with valgrind

Since e2image can be optionally compiled out, we tested to see if
e2image was built; but using "test -x $E2IMAGE" fails if e2image is
something like "valgrind --simhints=lax-ioctls ../misc/e2image".
Define and use $E2IMAGE_EXE, much like we have done with e2undo and
resize2fs.

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