oeqa/selftest/wic: Add ext4 to IMAGE_FSTYPES in test_exclude_path_with_extra_space

oeqa/selftest/wic: Add ext4 to IMAGE_FSTYPES in test_exclude_path_with_extra_space

All qemu machines have ext4 in IMAGE_FSTYPES which makes
native mkfs.ext4 available at wic image build time.
genericarm64 defaults to only wic in IMAGE_FSTYPES
and this test was failing:

| DEBUG: Python function extend_recipe_sysroot finished
| DEBUG: Executing python function set_image_size
| DEBUG: 148548.400000 = 114268 * 1.300000
| DEBUG: 652644.400000 = max(148548.400000, 8192)[148548.400000] + 504096
| DEBUG: 652645.000000 = int(652644.400000)
| DEBUG: 652645 = aligned(652645)
| DEBUG: returning 652645
| DEBUG: Python function set_image_size finished
| DEBUG: Executing shell function do_image_wic
| INFO: Creating image(s)...
|
| ERROR: A native program mkfs.ext4 required to build the image was not found (see details above).
|
| Please make sure wic-tools have e2fsprogs-native in its DEPENDS, build it with 'bitbake wic-tools' and try again.
|
| WARNING: exit code 1 from a shell command.
NOTE: recipe core-image-minimal-1.0-r0: task do_image_wic: Failed

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>