Add black magic to minimize ping losses

This particular arping interval/count, along with forcing it to run in
the foreground, seems to minimize the packet loss when the primary
coordinator transitions. Through extensive testing, this value results
in the, consistently, least amount of loss: 1-2 pings, at an 0.025s ping
interval, return "TTL exceeded", with no other loss, and only when the
node the test VM is on is the one switching to secondary state. No other
combination of values here, nor tweaks to other parts of the code, seem
able to reduce this further, therefore this is likely the best
configuration possible.

node-daemon/pvcd/common.py

@@ -119,11 +119,10 @@ def createIPAddress(ipaddr, cidrnetmask, dev):
         )
     )
     run_os_command(
-        'arping -P -U -W 0.2 -c5 -i {dev} -S {ip} {ip}'.format(
+        'arping -P -U -W 0.02 -c 2 -i {dev} -S {ip} {ip}'.format(
             dev=dev,
             ip=ipaddr
-        ),
-        background=True
+        )
     )
 
 # Remove IP address