mcc: replace cttypes with ign v3 types

[kikisdeliveryservice]

Just making this for future change:
Once ign v3_0 is release replace cttypes in transpiling to ign functions (ssh, files, systemd units in render.go) with http://github.com/coreos/ignition/config/v3_0/types - to be created.

cc: @runcom @ajeddeloh

[kikisdeliveryservice]

this is being addressed by #583
/assign

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