cluster scrape result not sent if single subressource could not be processed

[k15r]

Description

KMC must send partial data even if processing a single resource fails:

for example:

• redis parsing fails
• number of nodes and pvcs could be listed

expected result:

• any data which was able to get parsed should be send to the target system
• for failing data scrapes, the old values should be used
• for failing data scrapes, alerts shoul get triggered

[a-thaler]

A proposal on how to refactor the scraping mechanism is done at #123