Add save inventory thread for streaming refresh

[agrare]

This change adds a save inventory thread to help mitigate issues with lots of small updates overwhelm saving.

TODO: I'd like to concatenate the inventory collections which were queued so that e.g. hundreds of single changes are handled by a single refresh.

Depends:

• Streaming refresh refactoring #234

[Ladas]

@agrare dep merged, please rebase

we can talk later about the IC concat. To isolate the functionality, I would probably lean to Concatenate class, that would work with serialized ICs (Hash, parsed out of json). At this point it would be just merging of the hashes. What do you think?

[agrare]

@Ladas okay rebased

[kbrock]

extracting the saver is nice. adds some complexity, but it gives us a long desired need of merging duplicate refresh requests.

The saver is good as long as it is intended to be single threaded. And adding a mutex around ensure_saver_thread would make it thread safe. (overkill for now - and would just slow us down in the single threaded case)

[miq-bot]

Checked commit agrare@808284b with ruby 2.3.3, rubocop 0.52.1, haml-lint 0.20.0, and yamllint 1.10.0
3 files checked, 2 offenses detected

app/models/manageiq/providers/vmware/infra_manager/inventory/saver.rb

• ⚠️ - Line 82, Col 3 - Lint/HandleExceptions - Do not suppress exceptions.
• ❗ - Line 60, Col 3 - Style/RescueStandardError - Avoid rescuing without specifying an error class.

[Ladas]

probably some log here would be nice? we can do it in next PR

[Ladas]

Looks great