autofs: use safe xatol() and xatoi() helpers

Plus patch replaces atoi(32 bit) to xatol(64 bits) for "pipe_ino" mount
option thus fixing the issue with negative inode number for big values.

v2: fixed uninitialized "err" variable in "parse_options" function

Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>