fstools: media change detection (eg:sdcard) using kernel polling

fstools: media change detection (eg:sdcard) using kernel polling

Linux kernel has a polling mechanism that can be activated by changing
the parameter /sys/module/block/parameters/events_dfl_poll_msecs which
is deactivated by default or the /sys/block/[device]/events_poll_msecs
for one device.

This patch set the events_poll_msecs when a disk is inserted.
Once the media disk change event is sent by the kernel then we force a
re-read of the devices using /sbin/block info.

With this patch, insertion and ejection of sd card will automatically
generate partition devices in /dev.

Signed-off-by: Matthias Badaire <mbadaire@gmail.com>
[rewrap commit message, fix bashisms, fix non-matching condition,
 bump pkg release]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>