[docs] [output] meaningful message for healthcheck context exceeded.

[tejal29]

Relates to CI-CD health check docs.
Description
Give users more descriptive messge.

User facing changes

yes. Output lines changed. See below

Before
When Deployment did not stabilize, user will get an error message with

1. Either kubectl rollout status command killed (as timoutContext was cancelled)

tejaldesai@@getting-started (add_healthcheck)$ ../../out/skaffold deploy --status-check
Tags used in deployment:
Starting deploy...
kubectl client version: 1.11+
kubectl version 1.12.0 or greater is recommended for use with Skaffold
 - deployment.apps/getting-started created
Waiting for deployments to stabilize
 - default:deployment/getting-started Waiting for rollout to finish: 0 of 1 updated replicas are available...
 - default:deployment/getting-started failed. Error: kubectl rollout status command killed.
FATA[0006] 1/1 deployment(s) failed             

Or
2. an error message. "context deadline exceeded`.

tejaldesai@@getting-started (add_healthcheck)$ ../../out/skaffold deploy --status-check
Tags used in deployment:
Starting deploy...
kubectl client version: 1.11+
kubectl version 1.12.0 or greater is recommended for use with Skaffold
 - deployment.apps/getting-started configured
Waiting for deployments to stabilize
 - default:deployment/getting-started Waiting for rollout to finish: 1 old replicas are pending termination...
 - default:deployment/getting-started failed. Error: context deadline exceeded.
FATA[0006] 1/1 deployment(s) failed                     

After
New message:

- default:deployment/getting-started failed. Error: received Ctrl-C or deployments could not stabilize within 5s: kubectl rollout status command interrupted.

e.g.

tejaldesai@@getting-started (add_healthcheck)$ ../../out/skaffold deploy --status-check
Tags used in deployment:
Starting deploy...
kubectl client version: 1.11+
kubectl version 1.12.0 or greater is recommended for use with Skaffold
 - deployment.apps/getting-started created
Waiting for deployments to stabilize
 - default:deployment/getting-started Waiting for rollout to finish: 0 of 1 updated replicas are available...
 - default:deployment/getting-started failed. Error: received Ctrl-C or deployments could not stabilize within 5s: kubectl rollout status command interrupted.
FATA[0006] 1/1 deployment(s) failed                     
tejaldesai@@getting-started (add_healthcheck)$

Next PRs.
none

Submitter Checklist

Reviewer Notes

• The code flow looks good.
• Unit test added.
• User facing changes look good.

Release Notes

[codecov]

Codecov Report

Merging #3177 into master will decrease coverage by 0.01%.
The diff coverage is 50%.

Impacted Files	Coverage Δ
pkg/skaffold/deploy/resource/deployment.go	89.18% <0%> (-5.1%)	⬇️
pkg/skaffold/deploy/status_check.go	56.14% <100%> (+0.38%)	⬆️