Force Hard reboot re-create instance folder

When use share storage like ceph, instance's disk data is in ceph,
instance's disk doesn't rely on local instance folder anymore. So
when rebooting a instance, we should create the instance folder if
it is missed.

Change-Id: I1826d850cd802143e70e0e573ff061e12c6e5a4a
Upstream-Review: https://review.openstack.org/#/c/110524
Backported-from: juno
Closes-rally-bug: DE1351
Merge pull request #27 from TieWei/DE1351

Force Hard reboot re-create instance folder