DSL improvements: introduce sections in step declaration

[bugzmanov]

Background:
currently step declaration is messed up with: input values, export to context, flow specific details.
Export to context looks especially bad.

Proposal:

            provisionVms {
                phase = "provision"
                roleName = "erlangNode"
                hardwareId = "1"
                imageId = "5825"
                quantity = 2
                retryCount = 3
                exportTo = ["vms": "erlangServers"]
            }

change to

            provisionVms {
                execution: 
                   phase = "provision"
                   retryCount = 3
                input:    
                   roleName = "erlangNode"
                   hardwareId = "1"
                   imageId = "5825"
                   quantity = 2
                export:
                    vms as "erlangServers"
            }

Note: in case of step having onlu input parameters it should be possible to declare step without sections

More complex sample

[rsvato]

Actually, these sections are just labels, so you can use it without any modification, because they are skipped by Groovy parser. Export section is a little tricker. How about:

export:
vms to $context.erlangServers

?

as changed to 'to' to not interfere with cast operation?