Renamed sample with OpenStack provider

The deployment samples are located at doc/samples/deployments after when
a patch with separation of samples was merged.

Also, this patch contains renaming of sample devstack-lxc to
devstack-in-lxc for the reason to explicitly indicate difference between
a deploy engine and a server provider.

blueprint rally-docs

Change-Id: I9672fc217d012a29fc58297e738cf65d6e52c8a9
Merge "Renamed sample with OpenStack provider"