Add request timeout handling for Mellanox Neutron Agent

Add request timeout handling for messages sent to eswitch Daemon.
Using configurable number of retries and increasing waiting interval
between retries resend the message.
If request timeout persists, eswitch daemon is not reachable.
In such case, exit the agent process.

Closes-Bug: #1228827

Change-Id: If1290bedafe7a0dd8a61cbe328510075edeb1e5b
Removed erronus config file comment

The comment stating 'DHCP agents needs it.' with regards to the
rpc_notifier notification_driver is incorrect.  Looking through
the code, I see no place this is true.  I believe it to be an
error.

Closes-Bug: #1258390

Change-Id: I58c2f9290731f3e88e4b4a5bdb600aa5bac1a12b
Merge "Add request timeout handling for Mellanox Neutron Agent"
Merge "Removed erronus config file comment"