Automatic merge from submit-queue (batch tested with PRs 47896, 50678, 50620, 50631, 51005)
allow heapster option defaults to be set - kubectl top node|pod
**Release note**:
```release-note
NONE
```
Allows downstream / outside consumers of `NewCmdTopNode` and `NewCmdTopPod` commands to set project or case-specific heapster option defaults.
Related downstream PR: https://github.com/openshift/origin/pull/15764
cc @fabianofranz
* Rename variables and functions to match Go convention.
For example, UsageError --> UsageErrorf.
* Remove redundant or unreachable code.
* Simplify some utility functions (no functionality changes).
* Fix hanging 'if { return } else { return }' constructs.
* Fix several incorrect printf verbs.
OpenShift runs Heapster on HTTPS, which means `top node` and `top pod`
are broken because they hardcode 'http' as the scheme. Provide an
options struct allowing users to specify `--heapster-namespace`,
`--heapster-service`, `--heapster-scheme`, and `--heapster-port` to the
commands (leveraging the existing defaults).