Fix workaround for the "device is busy" problem

Right after partitioning, we have a sleep(3) to avoid the "device is
busy" problem. A less error-prone solution is to check with fuser,
whether there is any process currently using the disk.

The following config options are introduced under the 'disk_partitioner'
group:
- check_device_interval: seconds between consecutive checks for the
device status
- check_device_max_retries: number of retries for checking the device
status

Change-Id: Icb73db5aeb16d1abc390975c2bd8bf4b486566e5
Implements: blueprint device-status-check-with-fuser
Closes-Bug: #1301975
Merge "Fix workaround for the "device is busy" problem"