Fix asset test runner

[mtojek]

This PR adjusts the asset test runner with a couple of fixes.

Changes:

• ingest pipeline may be undefined to logs-type packages
• use asset ID from inside of a Kibana saved object file
• format loaded assets in failure message

[elasticmachine]

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Build stats

• Build Cause: Pull request #224 opened

• • Start Time: 2021-01-18T13:23:44.409+0000

• Duration: 12 min 59 sec

• Commit: 8487e86

Test stats 🧪

Test	Results
Failed	0
Passed	68
Skipped	0
Total	68

[mtojek]

self, approved. I need to fix elastic/integrations#536 .