core,journald: use quoted commandlines

I think quoting is more useful than not quoting. Without, arguments with
whitespace cannot be split correctly.

Unlike in coredump, "normal" quoting is used in those two cases. This output is
mostly for informational purposes, so the more readable quoting seems apropriate.

dbus GetProcesses:
$ busctl --user call org.freedesktop.systemd1 /org/freedesktop/systemd1/unit/run_2dr4450e1ae73944194bb6593fcfd255fbe_2eservice org.freedesktop.systemd1.Service GetProcesses
a(sus) 2
"/user.slice/user-1000.slice/user@1000.service/app.slice/run-r4450e1ae73944194bb6593fcfd255fbe.service" 131494 "/usr/bin/bash -c \"sleep 100; sleep 20\""
"/user.slice/user-1000.slice/user@1000.service/app.slice/run-r4450e1ae73944194bb6593fcfd255fbe.service" 131496 "sleep 100"