Add custom constructors to beta.3
Add custom constructors to beta.3

Currently every API object has a default constructor, `new()`, which
takes no arguments. Usually it is possible to make a better constructor.
This commit introduces many such convenience constructors.

Signed-off-by: Alex Clemmer <2e6147cbff6661bd424c256de746b4f230002dff@gmail.com>

ksonnet/ksonnet-lib,heptio/kube.libsonnet,ksonnet/ksonnet-lib