Fix installflags change detection

[kke]

Fixes #779

There was plenty of problems in the existing implementation:

• Incorrectly parsed the kubelet extra args value because the regexp cut it at the first space
• Omitted "--" in the parsed flags (because of the regexp)
• Inconsistent quoting/unquoting/splitting

Fixed by importing a couple of functions from rig v2 and getting rid of the regexp altogether.