libnm: Drop a wrong assert

An active connection object could disappear from the bus before its removal
from NMManager:active-connections is signalled -- don't assert it's gone from
there already.

Here /o/fd/NM/ActiveConnection/81 disappears shortly after it's added:

libnm-Message: PC: (0x9ebd088) NMManager:active-connections => '['/org/freedesktop/NetworkManager/ActiveConnection/81', '/org/freedesktop/NetworkManager/ActiveConnection/80']' (ao / NMActiveConnection)
libnm-Message: PC: (0x9ebd088) NMManager:activating-connection => ''/'' (o / NMActiveConnection)
libnm-Message: PC: (0x9ed1458) NMDeviceTeam:state => '110' (u)
libnm-Message: PC: (0x9ed1458) NMDeviceTeam:state-reason => '(110, 0)' ((uu))
libnm-Message: PC: (0x9ece9a0) NMActiveConnection:state => '3' (u)
libnm-Message: PC: (0x9ebd088) NMManager:state => '20' (u)
libnm-Message: PC: (0x9ebd088) NMManager:devices => '['/org/freedesktop/NetworkManager/Devices/0', '/org/freedesktop/NetworkManager/Devices/2', '/org/freedesktop/NetworkManager/Devices/3']' (ao / NMDevice)
libnm-Message: PC: (0x9ebd088) NMManager:active-connections => '['/org/freedesktop/NetworkManager/ActiveConnection/81', '/org/freedesktop/NetworkManager/ActiveConnection/80']' (ao / NMActiveConnection)
libnm-Message: PC: (0x9ece9a0) NMActiveConnection:state => '4' (u)
libnm-Message: PC: (0x9ece9a0) NMActiveConnection:devices => '[]' (ao / NMDevice)
libnm-Message: Could not create object for /org/freedesktop/NetworkManager/ActiveConnection/81: Method "GetAll" with signature "s" on interface "org.freedesktop.DBus.Properties" doesn't exist

(process:18042): libnm-CRITICAL **: object_creation_failed: assertion 'find_active_connection_by_path (self, failed_path) == NULL' failed
libnm: Complete activation when ActiveConnection abruptly disappears

A NMActiveConnection may disappear before a match with NMDevice is found. In
such case recheck_pending_activations() would never call the activation
callback and the client would hang indefinitely:

libnm-Message: PC: (0x95bf088) NMManager:active-connections => '['/org/freedesktop/NetworkManager/ActiveConnection/225']' (ao / NMActiveConnection)
libnm-Message: PC: (0x95bf088) NMManager:activating-connection => ''/'' (o / NMActiveConnection)
libnm-Message: PC: (0x95d0a28) NMActiveConnection:state => '4' (u)
libnm-Message: PC: (0x95d0a28) NMActiveConnection:devices => '[]' (ao / NMDevice)
libnm-Message: PC: (0x95bf088) NMManager:active-connections => '[]' (ao / NMActiveConnection)
*hang*

Let's listen for active-connection-removed and tear down the activation with
an error if the removed connection is one we're activating.
connections: Don't give up if we've not seen an active connection yet

It will appear later on.

https://bugzilla.redhat.com/show_bug.cgi?id=1149200
team: Don't let teamd rip off the link when it terminates

We might be reactivating a connection on the device and don't want it to go
away. In other cases we still take care of the link deletion ourselves.
device:  Don't delete the link if a re-activation is scheduled
cli: Only escape VPN banner if it's present

If the connection is in ACTIVATING state, the banner is still NULL.
vpn: Reuse last IP configuration if the helper didn't update the address

OpenVPN by default "resets" the connection after 120 seconds of not seeing a traffic
from remote (see openvpn --ping-restart option) to keep the connection alive if the
remote address changed. It then calls the helper, but only with subset of
configuration in the environment:

(gdb) p config_hash
$5 = 0x82dcab8 = {[0x82a6de0] = 0x82c6718, [0x8278768] = 0x8289da0, [0x82af690] = 0x8258430}
(gdb) print (char *)0x82a6de0
$6 = 0x82a6de0 "prefix"
(gdb) print (char *)0x8278768
$7 = 0x8278768 "tundev"
(gdb) print (char *)0x82af690
$8 = 0x82af690 "mtu"
(gdb)

This makes NetworkManager unhappy:

NetworkManager[497]: <error> [1415454333.569479] [vpn-manager/nm-vpn-connection.c:1187] nm_vpn_connection_ip4_config_get(): invalid IP4 config received!

Let's not tear down the connection due to lack of address, but reuse the existing
one.
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
Merge remote-tracking branches 'lr/lr-unmanaged-slaves', 'fd/lr/ipv6-tokens', 'fd/lr/team-activation' and 'fd/lr/openvpn' into integration