paritionedfs: partially fix extended paritions support

paritionedfs: partially fix extended paritions support

Currently MIC is unable to create more than 3 partitions, because the
logical/extended paritions support is broken. This is because the EBR is not
taken into account, so parted fails to create logical partitions. EBR stands
for "Extended Boot Record" and this ia basically a single sector which prepends
every logical parition.

This patch fixes the issue. We take one sector from each partition starting
from the 3rd one (the last primary parition), and this sector will be used by
parted for the EBR. This works nicely and partitions stay aligned correctly for
the best performance.

Change-Id: I678c52f24750388ffdc09c32939541ba3f3e8b8f
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>