Add debug information for engine workflow
Add debug information for engine workflow

This patch adds debug information for some engine
workflows, like cluster_create, cluster_resize, etc.
These debug information will be helpful for operator
and developer to track the workflow executed inside
senlin-engine.
It also changes the log level of some existing debug
info from ERROR to DEBUG since they are actually for
errors like badrequest from enduser rather than
exceptions of senlin-engine itself.

Change-Id: I68f655cea382fbb5443a317260fc473040426e4e
Closes-Bug: #1592736

stackforge/senlin,openstack/senlin,openstack/senlin,stackforge/senlin,openstack/senlin