fs-tests: integck: Refactor: split out common remount logic

fs-tests: integck: Refactor: split out common remount logic

remount_tested_fs() and recover_tested_fs() both have
almost the same code for remounting the target FS
RO then RW. Split this sequence into a new
function called remount_ro_rw().

Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Link: https://lore.kernel.org/linux-mtd/5530437c-b564-461f-26af-85bde1a00cb3@huawei.com/T/#mad1d043095b3f64a1f1eddd2d87b1545e329e141
Signed-off-by: Csókás, Bence <csokas.bence@prolan.hu>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>