libvirt: bump master memory to 4096 MB

[rphillips]

On my development machine (libvirt) the master has started to swap after a few minutes of being up. This patch bumps the memory to 4096MB and is currently stable.

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[cgwalters]

Overlaps #785

(Also random aside; RHCOS doesn't ship with swap enabled, it isn't recommended for Kubernetes - the kswap0 process you're seeing is background writeback )

[rphillips]

nice. closing in favor of the other PR