feat(dbus): make API synchronous and remove assumptions
feat(dbus): make API synchronous and remove assumptions

Previously, this library assumed all jobs would be started/stopped/etc
with "replace" as the mode string.  There is no reason to make this
assumption.

mischief/go-systemd,philips/go-systemd-old,faiq/go-systemd,pquerna/go-systemd,jonboulle/go-systemd,ZeissS/go-systemd,jareksm/go-systemd,jonboulle/go-systemd,coreos/go-systemd,glerchundi/go-systemd,mischief/go-systemd,lemenkov/go-systemd,coreos/go-systemd,faiq/go-systemd,pquerna/go-systemd,endocode/go-systemd,tianon/debian-golang-go-systemd,glerchundi/go-systemd,jareksm/go-systemd,mikkeloscar/go-systemd,endocode/go-systemd,lemenkov/go-systemd,pcarranzav/go-systemd,tianon/debian-golang-go-systemd,dnaeon/go-systemd,Yhgenomics/go-systemd,mikkeloscar/go-systemd,pcarranzav/go-systemd,brnv/go-systemd,Yhgenomics/go-systemd,brnv/go-systemd,ZeissS/go-systemd,dnaeon/go-systemd