e2fsprogs: fix test f_detect_junk print error msg

e2fsprogs: fix test f_detect_junk print error msg

This test need to check config.h, so install it
to fix below err msg:

grep: ../lib/config.h: No such file or directory
./test/f_detect_junk/script: line 3: [: : integer expression expected
f_detect_junk: detect non-fs file data: ok

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>