Metric::Rollup - simplify column declarations

[kbrock]

3 commits:

• Metric::Rollup: dedup common rollup aggregate column lists
• extract Metric::Rollup#aggregate_column
• drop VimPerformanceState special case for looking up EmsCluster#vms

[kbrock]

WIP: not sure that the aggregation is correct for EmsCluster. So the change may not be valid.

TODO: verify that aggregation is working, then verify if the vms are the same thing.

[kbrock]

UN-WIP: removed EmsCluster changes.

so this PR is now just the 2 refactors around rollup

[Fryguy]

The first set is really around container usage, not vm usage. Also it includes more than CPU. Also, also the pattern is to use the phrase ROLLUP_COLS (aside from storage), so I'm thinking rename to something like:

Suggested change

	BASIC_VM_CPU_COLS = [:cpu_usage_rate_average, :derived_vm_numvcpus, :derived_memory_used, :net_usage_rate_average].freeze
	BASIC_VM_DISK_COLS = [:cpu_usage_rate_average, :derived_memory_used, :disk_usage_rate_average, :net_usage_rate_average].freeze
	CONTAINER_ROLLUP_COLS = [:cpu_usage_rate_average, :derived_vm_numvcpus, :derived_memory_used, :net_usage_rate_average].freeze
	VM_ROLLUP_COLS = [:cpu_usage_rate_average, :derived_memory_used, :disk_usage_rate_average, :net_usage_rate_average].freeze

[kbrock]

update:

• rebased (fix merge conflict)
• renamed constants

[miq-bot]

Checked commits kbrock/manageiq@d10075a~...9f6b517 with ruby 2.6.10, rubocop 1.28.2, haml-lint 0.35.0, and yamllint
1 file checked, 0 offenses detected
Everything looks fine. 🍪

[kbrock]

@Fryguy I think this is ready for merge. Probably without backport (since it is low risk, but no need to backport)