tests: rename commonlib function, update

Let's update `get_ip_for_nic()` to `get_ipv4_for_nic()` since we're
inspecting the ipv4 address. Let's also make it not use a shared
global variable but rather capture the return value from the function
call.

Author: dustymabe

tests/kola/data/commonlib.sh

@@ -12,12 +12,12 @@ fatal() {
     exit 1
 }
 
-get_ip_for_nic () {
+get_ipv4_for_nic() {
     local nic_name=$1
-    nic_ip=""
-    nic_ip=`ip -j addr show ${nic_name} | jq -r '.[0].addr_info | map(select(.family == "inet")) | .[0].local'`
-    if [ -z "$nic_ip" ]; then
-        echo "Error: can not get ${nic_name} ip"
+    local ip=$(ip -j addr show ${nic_name} | jq -r '.[0].addr_info | map(select(.family == "inet")) | .[0].local')
+    if [ -z "$ip" ]; then
+        echo "Error: can not get ip for ${nic_name}"
         exit 1
     fi
+    echo $ip
 }

tests/kola/networking/force-persist-ip/test.sh

@@ -17,8 +17,7 @@ set -xeuo pipefail
 
 # Verify ens5 get staic ip via kargs
 nic_name="ens5"
-nic_ip=""
-get_ip_for_nic ${nic_name}
+nic_ip=$(get_ipv4_for_nic ${nic_name})
 if [ ${nic_ip} != "10.10.10.10" ]; then
     fatal "Error: get ${nic_name} ip = ${nic_ip}, expected is 10.10.10.10"
 fi

tests/kola/networking/prefer-ignition-networking/test.sh

@@ -17,8 +17,7 @@ set -xeuo pipefail
 
 # Verify ens5 get ip address via dhcp
 nic_name="ens5"
-nic_ip=""
-get_ip_for_nic ${nic_name}
+nic_ip=$(get_ipv4_for_nic ${nic_name})
 if [ ${nic_ip} != "10.0.2.31" ]; then
     fatal "Error: get ${nic_name} ip = ${nic_ip}, expected is 10.0.2.31"
 fi