pillar: Add new Makefile targets for Docker dev builds and shell access. #1887

Job	Run time
packages (arm64-secure, arm64)	7m 46s
packages (ubuntu-20.04, amd64)	5m 1s
packages (ubuntu-latest, riscv64)	2m 43s
eve (arm64, kvm)	30m 40s
eve (arm64, xen)	29m 17s
eve (amd64, kvm)	32m 30s
manifest	2m 58s
verification (arm64, kvm)	7m 21s
eve (amd64, xen)	30m 41s
verification (arm64, xen)	7m 6s
verification (amd64, kvm)	8m 24s
verification (amd64, xen)	7m 12s
eve (riscv64, mini)	3m 33s
trigger_assets	0s
	2h 55m 12s

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