Bug 1460206

Description of problem: 
cloud-init can't find Azure endpoint server during provisioning on Azure Platform,and then cause cloud-init to use "DataSourceNone" as its datasource(this value is fallback value).
cloud-init find Azure endpoint server in  "/run/cloud-init/dhclient.hooks" folder, this folder and file in this folder is generated by "/etc/NetworkManager/dispatcher.d/cloud-init-azure-hook".
The file is a hook script,and it will be invoked by NetworkManager during booting.But the hook script will check whether there is a marker file under /run/cloud-init,called "enabled".
If the marker file doesn't exist,the hook script will not generate "/run/cloud-init/dhclient.hooks" folder and files in this folder.And the marker file is generated by a systemd generator "/usr/lib/systemd/system-generators/cloud-init-generator".
From 0.7.9-5, we remove the generator,so the marker will not exist,and finally cause the issue.

So....in a word,
due to "/usr/lib/systemd/system-generators/cloud-init-generator" was removed 
       ==> not generate marker file "/run/cloud-init/enabled"
           ==> NetworkManager hook script will not execute dhcp hook
               ==> not generator "/run/cloud-init/dhclient.hooks"
                   ==> cloud-init can't find Azure endpoint server

the content of "/etc/NetworkManager/dispatcher.d/cloud-init-azure-hook" is below,the keypoint I have highlighted
#!/bin/sh
# This file is part of cloud-init. See LICENSE file for license information.

# This script hooks into NetworkManager(8) via its scripts
# arguments are 'interface-name' and 'action'
#
is_azure() {
    local dmi_path="/sys/class/dmi/id/board_vendor" vendor=""
    if [ -e "$dmi_path" ] && read vendor < "$dmi_path"; then
        [ "$vendor" = "Microsoft Corporation" ] && return 0
    fi
    return 1
}

is_enabled() {
    # only execute hooks if cloud-init is enabled and on azure
    [ -e /run/cloud-init/enabled ] || return 1
    is_azure
}


if is_enabled; then
    case "$1:$2" in
        *:up) exec cloud-init dhclient-hook up "$1";;
        *:down) exec cloud-init dhclient-hook down "$1";;
    esac
fi


### Why do we remove the generator?
refer this link: https://bugzilla.redhat.com/show_bug.cgi?id=1440831


Version-Release number of selected component (if applicable): 
cloud-init-0.7.9-5.el7.x86_64.rpm(the latest build is 0.7.9-8) 

RHEL Version: 
RHEL-7.4

How reproducible: 
100%

Steps to Reproduce: 
1. Prepare a running VM in Azure. Install cloud-init-0.7.9-8.el7.x86_64.rpm
2. Add a new user and this user must authenticate by keypair(not use password),and this user have sudo privilege.
    (This step can ensure you can successfully login the VM,even though provision process failed)
3. systemctl enable cloud-{init,init-local,config,final}
4. Change /etc/waagent.conf, set Provisioning.Enabled=n, Provisioning.UseCloudInit=y
5. Deprovision this VM use WALA,and use this VM as a template to create a new VM
6. After provision finishing,login the VM
7. Check if cloud-init does provisioning successfully

Actual results: 
cloud-init doesn't successfully provision(cloud-init can't find Azure endpoint server,and use fallback value "DataSourceNone")

......
2017-06-09 11:09:38,303 - azure.py[INFO]: Registering with Azure...
2017-06-09 11:09:38,303 - azure.py[DEBUG]: Finding Azure endpoint...
2017-06-09 11:09:38,304 - util.py[DEBUG]: Reading from /etc/cloud/cloud.cfg (quiet=False)
2017-06-09 11:09:38,304 - util.py[DEBUG]: Read 1150 bytes from /etc/cloud/cloud.cfg
2017-06-09 11:09:38,304 - util.py[DEBUG]: Attempting to load yaml from string of length 1150 with allowed root types (<type 'dict'>,)
2017-06-09 11:09:38,325 - util.py[DEBUG]: Reading from /etc/cloud/cloud.cfg.d/05_logging.cfg (quiet=False)
2017-06-09 11:09:38,325 - util.py[DEBUG]: Read 1821 bytes from /etc/cloud/cloud.cfg.d/05_logging.cfg
2017-06-09 11:09:38,325 - util.py[DEBUG]: Attempting to load yaml from string of length 1821 with allowed root types (<type 'dict'>,)
2017-06-09 11:09:38,334 - util.py[DEBUG]: Attempting to load yaml from string of length 0 with allowed root types (<type 'dict'>,)
2017-06-09 11:09:38,334 - util.py[DEBUG]: load_yaml given empty string, returning default
2017-06-09 11:09:38,335 - azure.py[DEBUG]: /run/cloud-init/dhclient.hooks not found.
2017-06-09 11:09:38,335 - azure.py[DEBUG]: Unable to find endpoint in dhclient logs.  Falling back to check lease files
2017-06-09 11:09:38,336 - azure.py[DEBUG]: Looking for endpoint in lease file /var/lib/dhcp/dhclient.eth0.leases
2017-06-09 11:09:38,336 - util.py[DEBUG]: Reading from /var/lib/dhcp/dhclient.eth0.leases (quiet=False)
......
2017-06-09 18:05:38,819 - DataSourceAzure.py[INFO]: Error communicating with Azure fabric; assume we aren't on Azure.
......


Expected results: 
cloud-init successfully provision

Additional info: