[patch] Add ability to set maxUnavailable for machine configs

[IanBoden]

Issue

Airgap testing is unreliable - no specific issue created

Description

Airgap tests were hitting two problems:

1. fyre login sometimes failing the first time - the roks login task would retry so copied the settings from there
2. setup frequently taking more than 2 hours and the pipeline timing it out - by updating worker nodes in parallel the time has roughly halved

Test Results

Tested by ongoing daily runs, will take time to see how much this improves stability but initial testing shows promise

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[durera]

Nice idea!