Unit Test - servicedeployer.go

Add unit tests to validate methods under deployers package which are defined in [servicedeployer.go](https://github.com/apache/incubator-openwhisk-wskdeploy/blob/master/deployers/servicedeployer.go).

All unit tests should go in servicedeployer_test.go under [deployers/](https://github.com/apache/incubator-openwhisk-wskdeploy/blob/master/deployers)

```
// check to validate manifest and deployment files are valid and could be parsed
func (deployer *ServiceDeployer) Check() {
...
}

// parse manifest and deployment files and determine the openwhisk entities involved to deploy
func (deployer *ServiceDeployer) ConstructDeploymentPlan() error {
...
}

// parse manifest and deployment files and determine the openwhisk entities involved to undeploy
func (deployer *ServiceDeployer) ConstructUnDeploymentPlan() (*DeploymentApplication, error) {
...
}

// deploy all the entities specified in manifest and deployment file
// its not trivial to create unit tests for this method, try to figure out if we can create some kind of mock
// else we can move this under integration testing
func (deployer *ServiceDeployer) Deploy() error {
...
}

// deploy entities specified in manifest and deployment file
// similar to Deploy method, we can move this under integration testing if needed
func (deployer *ServiceDeployer) UnDeploy(verifiedPlan *DeploymentApplication) error {
...
}

```