Add support for scaling application containers

[devdattakulkarni]

We should support a command for scaling application containers. Something like,

cld app scale {app-name} {target-number-of-instances}

For multi-container applications the scale command should work against individual microservice container. We will need to add a 'service' abstraction first.

cld service scale {service-name} {target-number-of-instances}