DHCP: make udev rules want dhcp-interface@.service

Updates the dhcp-all-interfaces element to fix a race
with the recent udev rules implementation on Fedora.

With the new approach we make the udev rule want (require
to startup) a generic dhcp-interface@.service template which
can be started individually for each interface that is
discovered.

The dhcp-interface@.service is setup such that it:

1) It calls dhcp-all-interfaces <iface> directly with
 a pre-exec script. This creates the ifcfg file right
 before we need it but avoids the case where network.service
 might get greedy and try to start it itself.

2) Only runs if the ifcfg script doesn't already exist. This
 is important because we only need to bootstrap the DHCP configs...
 Once they exist the network.service will take care of starting them
 on reboots, upgrades, etc.

3) On initial boot ensure that the initial DHCP interfaces come
 up after network.service. Since we really only want
 dhcp-all-interfaces to help bootstrap that haven't already
 been configured this seems reasonable.

4) We also try to ensure that cloud-init
 comes up after the DHCP interfaces. Cloud init has a decently
 long timeout that this wasn't a functional problem but it keeps
 log file spew down.

Change-Id: I71b026f027182aad49c3435bb903e5e38e524685
Closes-bug: #1294803
Set +x on executable files

Change-Id: I6007aa3f4e6326b1c7030ad0463c7e8f49fbd507
Merge "DHCP: make udev rules want dhcp-interface@.service"
Merge "Set +x on executable files"