Add status conditions helpers

[joelanford]

Description of the change:
This PR adds status condition helpers that simplify setting and checking conditions on CR status fields.

Motivation for the change:
To promote the use of status conditions and to help users implement them consistently and according to best practices.

[joelanford]

Submitted upstream issue: kubernetes-sigs/controller-tools#155

[joelanford]

As suggested by @shawn-hurley, I tried using a typed slice for the status conditions helper and implementing the same set of methods that are on the struct (see commit 4f8388a).

type ConditionsSlice []Condition

Unfortunately, that also fails during operator-sdk generate openapi:

E0306 12:39:33.837821 30846 openapi.go:294] Error when generating: conditions, Conditions github.com/operator-framework/operator-sdk/pkg/status.ConditionsSlice
2019/03/06 12:39:33 OpenAPI code generation error: Failed executing generator: some packages had errors:
slice Element kind Interface is not supported in []github.com/operator-framework/operator-sdk/pkg/status.Condition

I traced that error back to here: https://github.com/kubernetes/kube-openapi/blob/15615b16d372105f0c69ff47dfe7402926a65aaa/pkg/generators/openapi.go#L624

It looks like there's potential for upstream work related to this error as well. For example, the openapi.OpenAPIDefinitionGetter interface looks promising, but so far I haven't been able to figure out how to hook into anything that calls it.

[jmccormick2001]

/lgtm - is any user facing documentation required for this change?

[estroz]

New file license years need to be changed, and 2 suggestions. Overall LGTM.

[joelanford]

@jmccormick2001 Good point, I'll see if I can find a spot to mention this. Maybe in the user guide.

I tried to make the GoDoc comments pretty verbose/descriptive since this is mainly a bunch of optional helpers in a library, but it is helpful and is worth highlighting in a user-facing doc as well.

[estroz]

Just grammar nits, otherwise

/lgtm

[openshift-ci-robot]

New changes are detected. LGTM label has been removed.