fs/ext4-new-features: add ext4-new-features tests to default

Remove run_ext4_test.sh which calls all feature tests directly.
Now we treat every feature as a signle test in fs_ext4 runtest file,
keep one entry per test.
Like that:
	ext4-nsec-timestamps    ext4_nsec_timestamps_test.sh
	ext4-uninit-groups      ext4_uninit_groups_test.sh

Configure script has been removed and ffsb has been moved to utils directory.

If want to run these tests, user should specify a big block device
when running runltp script.

Currently enable ext4-nsec-timestamps, ext4-persist-prealloc,
ext4-subdir-limit, ext4-uninit-groups test.

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>