switch-to-configuration: Honour RefuseManualStop

This prevents spurious errors about systemd-tmpfiles-setup.service.

Backport: 14.04
(cherry picked from commit bac68f974721f07faebe749df8162f641e5d4528)
sysinit.target: Don't depend on systemd-tmpfiles-setup.service

systemd-tmpfiles-setup.service pulls in local-fs.target, which
interferes with NixOps' send-keys feature (since sshd.service depends
indirectly on sysinit.target). Since in NixOS we don't use
systemd-tmpfiles for creating files (that's done by activation scripts
and preStart scripts), it's not a problem to start it a bit later.

Backport: 14.04
(cherry picked from commit 014fe1a3c3877360b1e43540ccb9242a845bba10)
Don't start getty@tty1 on headless machines (like EC2)

Backport: 14.04
(cherry picked from commit 4a08f3720635b7bb3b46dea80bba491302b16f68)
systemd-journal-flush: Require /var/log/journal rather than all filesystems

Backport: 14.04
(cherry picked from commit 24cbe874d6b97a6471b51bcbca956910d92fea9b)
Don't run hwclock if /dev/rtc doesn't exist

E.g. on EC2 instances.

Backport: 14.04
(cherry picked from commit 5bfe944907b0afcc979e4db7058cbfd884fd029b)