cluster-autoscaler: standardize context usage

[jackfrancis]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

This PR standardizes CA-specific context usage of the "k8s.io/autoscaler/cluster-autoscaler/context" library.

Specifically:

• Standardize the import reference to ca_context to disambiguate from the standard golang "context" package.
  • e.g., ca_context "k8s.io/autoscaler/cluster-autoscaler/context"
• Standardize variable references to type AutoscalingContext in functions, etc, as autoscalingContext (again, to disambiguate from the standard context foo)
• Undo any non-idiomatic usage of the standard golang "context" package
  • e.g., we always import as "context", and never with an alias
  • e.g., we always use ctx as the variable reference to a context.Context type

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: jackfrancis
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[jackfrancis]

/assign @MaciekPytel @towca

While reviewing some other PRs this stuff was driving me nuts. I think this PR, while pretty huge, improves the way we use context(s) significantly and isn't too horrible to review.

[jackfrancis]

/test ls

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[jackfrancis]

/test pull-cluster-autoscaler-e2e-azure-master