platform/machine/aws: merge pre/post-termination console logs
platform/machine/aws: merge pre/post-termination console logs

GetConsoleOutput only returns 64 KB, which is not quite enough for a
complete boot + shutdown cycle. If we have two sets of logs, merge them.

glevand/coreos--mantle,dm0-/mantle,dm0-/mantle,glevand/coreos--mantle