DHCPv4 can fail for two reasons:

 (a) the client failed to contact server and to get an initial lease

 (b) the client failed to renew the lease after it was successfully
     acquired

For (a) the client generates a TIMEOUT event, for (b) an EXPIRED
event.  Currently we fail the IP method immediately after (a), but
this doesn't work well when the carrier flickers and we restart the
client because if the server goes temporarily down, the IP method
fails and DHCP is never restarted.

Let's change this, and determine whether to fail IP configuration only
by looking at the current IP state: when it's IP_CONF then we are
getting the initial lease and a failure means that IP configuration
must fail; otherwise any other state means that the lease expired or
could not be renewed and thus we keep the client running for the grace
period.

https://bugzilla.redhat.com/show_bug.cgi?id=1573780