When init starts daemons through a shell script, replace the shell altogether

A few daemons are being started from init through a shell script. Since the daemon does not "deamonizes" properly, it's been put in the background from the shell by using ( ... ) &, however this leaves a lingering shell that serves no purpose. This patch improves this situation.

The situation before this change looked like:

    init-+-Xorg
         |-avahi-daemon
         |-console-kit-dae-+-62*[{console-kit-da}]
         |                 `-{gdbus}
         |-dbus-daemon
         |-eventlircd
         |-klogd
:        |-init---atvclient
         |-init---connmand
:        |-init---ratpoison
:        |-init---udevadm
         |-polkitd---{gdbus}
         |-rpcbind
         |-sshd---sshd---sh---pstree
         |-syslogd
         |-systemd-udevd
:        |-tvheadend.start---tvheadend---12*[{tvheadend}]
         |-udisks-daemon-+-udisks-daemon
         |               |-{gdbus}
         |               `-{gmain}
         |-upowerd-+-{gdbus}
         |         `-{gmain}
         |-wpa_supplicant
         `-xbmc.bin---17*[{xbmc.bin}]

After this change, it looks like:

    init-+-Xorg
:        |-atvclient
         |-avahi-daemon
         |-console-kit-dae-+-62*[{console-kit-da}]
         |                 `-{gdbus}
         |-dbus-daemon
         |-eventlircd
         |-init---connmand
         |-klogd
         |-polkitd---{gdbus}
:        |-ratpoison
         |-rpcbind
         |-sshd---sshd---sh---pstree
         |-syslogd
         |-systemd-udevd
:        |-tvheadend---12*[{tvheadend}]
:        |-udevadm
         |-udisks-daemon-+-udisks-daemon
         |               |-{gdbus}
         |               `-{gmain}
         |-upowerd-+-{gdbus}
         |         `-{gmain}
         |-wpa_supplicant
         `-xbmc.bin---17*[{xbmc.bin}]

Only for connmand this is not easily done since the shell loops and restarts connmand. In different circumstances /etc/inittab would respawn the process.
Merge pull request #1855 from dagwieers/exec-daemon

When init starts daemons through a shell script, replace the shell altogether