tests: ubifs_tools: fsck_tests: Add powercut+fsck+mount test

tests: ubifs_tools: fsck_tests: Add powercut+fsck+mount test

Inject powercut while doing fsstress on mounted UBIFS for kinds of
flashes (eg. nand, nor).
This testcase mainly makes sure that fsck.ubifs can make UBIFS image
be consistent on different flashes (eg. nand, nor). Because the
min_io_size of nor flash is 1, the UBIFS image on nor flash will be
different from nand flash after doing powercut, so we need make sure
fsck.ubifs can handle these two types of flash.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>