I ran into this issue today that the Controller provisioning fails with "Failed to power on VM NSX Controller".

NSX Manager log contains:

Caused by: com.vmware.vshield.vsm.inventory.vcoperations.VcTaskFailureException: core-services:1501:The task failed on VC. For more details, refer to the rootCauseString or the VC logs:A general system error occurred: Connection refused.

But only the VPXD log helped to shed some light:

2015-10-16T15:42:40.281Z error vpxd[7FAF7D2C9700] [Originator@6876 sub=HttpConnectionPool-000001] [ConnectComplete] Connect failed to <cs p:00007fafa4221ed0, TCP:localhost:8088>; cnx: (null), error: N7Vmacore15SystemExceptionE(Connection refused)
2015-10-16T15:42:40.281Z error vpxd[7FAF8C1BB700] [Originator@6876 sub=WorkflowRedirection opID=22fb315a] [WorkflowRedirectCallback] Workflow manager returned exception: N7Vmacore15SystemExceptionE(Connection refused)

The Windows service VMware vCenter workflow manager failed and needed to be restarted.