Use oslo.utils.netutils function to set tcp_keepalive

Use netutils.set_tcp_keepalive to set tcp keepalive parameters.
In addition to the existing conf option for tcp_keepidle, new
values were added for tcp_keepalive (to turn on/off this feature,
tcp_keepalive_interval (to specify gap between successive probes) and
tcp_keepalive_count (to specify number of probes).

Change-Id: I60c3bbf5f3deff8bdffe97af76052386e4598b45
Merge "Use oslo.utils.netutils function to set tcp_keepalive"