make_fs(): add tunefs -e remount-ro

As suggested in bug #3025, it is good to remount ploop inner filesystem
read-only as soon as kernel sees it is corrupted, in order to prevent
any more damage.

https://bugzilla.openvz.org/3025

Reported-by: Pavel Odintsov <pavel.odintsov@gmail.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
ploop_check: fixed reopen fd logic

This is a fix to commit 1bfbe42.

Reference: ploop@1037051
[style] check.c: rearrange code to remove function declaration

move up:
static int reopen_rw(const char *image, int *fd);
static int fill_hole(const char *image, int *fd, off_t start, off_t end, int *log, int repair);
static int check_and_repair_sparse(const char *image, int fd, __u64 cluster, int flags);

Reference: ploop@1037054
ploop_check(): use reopen_rw()

1. reopen_rw(): check the result of close(), reassign new fd
2. modify check_and_repair_sparse to use *fd not fd
3. use reopen_rw() in ploop_check()

Reference: ploop@1037067
ploop info help: add -d

This is an addition to commit 0b51f0d.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>