fs-tests: integck: add recovery remounting function

fs-tests: integck: add recovery remounting function

When re-mountig to recover from the emulated power-cut failure then we should
do a bit less fancy things, e.g., we should not try to re-mount to R/O and R/W
modes forth and back, but we should instead just unmount directly.

Additionally, we should not die if mount fails because there may be a power
cut emulation during mounting. Thus, create a separate function for recovering
and try to recover in a loop.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>