--start parameter will be used to specify start endpoint
for tasks execution based on graph traversal
Examples:
fuel node --node 2,3 --start netconfig
fuel node --node 2,3 --start netconfig --end neutron
Patch-Set in nailgun: I4d7c9ec825d9534ce3aafd218716e6045915e5a0
implements blueprint granular-deployment-based-on-tasks
Change-Id: Iccc9555f532858e9df67d4dbd10856c1e7f8afd9