rename Set* to set* in manifestreader.go

There are few set methods in [manifestreader.go](https://github.com/apache/incubator-openwhisk-wskdeploy/blob/master/deployers/manifestreader.go) which only have single usage inside the same manifestreader.go file. There is no need to export following methods outside of deployer package. Rename them to set* to mark it as unexported.

SetDependencies to setDependencies
SetPackage to setPackage
SetActions to setActions
SetSequences to setSequences
SetTriggers to setTriggers
SetRules to setRules
SetApis to setApis