Medium: Raid1: do not test for device existence in the stop operation (bnc#821861)

Sometimes udevd may not react quickly enough and remove the
devices, hence the stop operation may unnecessarily fail. Whether
a device file exists or not is anyway irrelevant when stopping.
Medium: Raid1: wait for udevd to settle (bnc#821861)

Sometimes udevd does not create devices as quickly as needed.
This patch introduces a new parameter (udev). If it's set to true
(which is also the default) it will invoke udevadm settle to wait
for udevd to finish creating the MD device. We also use
--exit-if-exists not to wait unnecessarily for other events.
Medium: Raid1: set MDADM_NO_UDEV appropriately if udev is not used
Medium: Raid1: stop arrays even with block device file missing (bnc#821861)

An MD array may be running, but the device file /dev/mdnn
missing (i.e. due to some udevd issue). This patch enables Raid1
to stop successfully such arrays.
Merge pull request #245 from dmuhamedagic/Raid1-udev

Raid1 udev create/remove device delay