cli: Only escape VPN banner if it's present

If the connection is in ACTIVATING state, the banner is still NULL.
vpn: Propagate daemon exec error correctly

NetworkManager[31624]: <warn>  VPN service 'openvpn': could not launch the VPN service. error: (8) Failed to execute child process "/usr/local/libexec/nm-openvpn-service" (No such file or directory).
**
NetworkManager:ERROR:nm-manager.c:3094:_activation_auth_done: assertion failed: (error)
libnm: Don't expect VPN connections to attach to the device
cli: Abort when given name of a non-existent connection for nmcli up

Even when ifname is present: nmcli c up name Nonexistent ifname wlan0
cli: Only construct an agent for a connection if there is a connection

[lkundrak@fedora20-2 ~]$ nmcli --ask c ifname wlan0

(process:18405): libnm-CRITICAL **: nm_object_get_path: assertion 'NM_IS_OBJECT (object)' failed
Error: Connection activation failed: The device has no connections available.
[lkundrak@fedora20-2 ~]$
cli: Watch for device as well as AC state changes when activating

The signals might be delivered in no particular order and we need to wait for
the device to reach stable state (whether it's successfully conntected or not)
as well as the active connection to leave ACTIVATING state.
device: Remove unmanaged slaves from master when they disappear

We've previously been just watching for state changes into UNMANAGED state. No
state change is emitted upon removal of a device which is already unmanaged.
device: Don't consider device with only LL address configured

LXC domains are given a veth interface that's up and has a LL address
upon their creation.
device,settings: don't assume the device is connected because it's software

It was possibly done to prevent NM from fiddling with the interface. However,
assuming a connection completely prevents the user from being able to use
their conneciton.

Let's just not add default connection to software devices.
Revert "core: make veth devices default-unmanaged for now"

veth devices being default unmanages makes it impossible to configure the
connectivity by NM on container bootup. Now that we don't add a default
connection when a veth is discovered is shouldn't be necessary to prevent
management anymore.

This reverts commit ebeaeaed4d3180c27cc059fe0ff199153fa9ec24.
fixup! cli: Watch for device as well as AC state changes when activating
Merge remote-tracking branches 'fd/lr/ipv6-tokens', 'fd/lr/nm-1-0-fixes', 'fd/lr/unmanaged-slaves', 'fd/lr/device-activation' and 'fd/lr/veth-managed' into integration