python: Write py3 bin to correct args location

python: Write py3 bin to correct args location

Comands written like this were working:
python /home/dmulder/code/samba/source4/scripting/bin/subunitrun
Changed to:
/usr/bin/python3 /home/dmulder/code/samba/source4/scripting/bin/subunitrun

But commands with env args overwrite the wrong arg:
CLIENT_IP=127.0.0.11 SOCKET_WRAPPER_DEFAULT_IFACE=11 python /home/dmulder/code/samba/source4/scripting/bin/subunitrun
Changed to:
/usr/bin/python3 SOCKET_WRAPPER_DEFAULT_IFACE=11 python /home/dmulder/code/samba/source4/scripting/bin/subunitrun
And were further mangled in plantestsuite_loadlist() to:
/usr/bin/python3 /home/dmulder/code/samba/source4/scripting/bin/subunitrun SOCKET_WRAPPER_DEFAULT_IFACE=11 python /home/dmulder/code/samba/source4/scripting/bin/subunitrun

Signed-off-by: David Mulder <dmulder@suse.com>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>