UPDATE command made generic.

Update command was hard-coded for debian or ubuntu based systems which was 'apt-get'. Setting an update variable accordingly solves this problem.

util/install.sh

@@ -40,6 +40,7 @@ if [ "$DIST" = "Ubuntu" ] || [ "$DIST" = "Debian" ]; then
     install='sudo DEBIAN_FRONTEND=noninteractive apt-get -y -q install'
     remove='sudo DEBIAN_FRONTEND=noninteractive apt-get -y -q remove'
     pkginst='sudo dpkg -i'
+    update='sudo apt-get'
     # Prereqs for this script
     if ! which lsb_release &> /dev/null; then
         $install lsb-release
@@ -51,6 +52,7 @@ if [ "$DIST" = "Fedora" -o "$DIST" = "RedHatEnterpriseServer" ]; then
     install='sudo yum -y install'
     remove='sudo yum -y erase'
     pkginst='sudo rpm -ivh'
+    update='sudo yum'
     # Prereqs for this script
     if ! which lsb_release &> /dev/null; then
         $install redhat-lsb-core
@@ -103,7 +105,7 @@ OF13_SWITCH_REV=${OF13_SWITCH_REV:-""}
 
 function kernel {
     echo "Install Mininet-compatible kernel if necessary"
-    sudo apt-get update
+    $update update
     if ! $install linux-image-$KERNEL_NAME; then
         echo "Could not install linux-image-$KERNEL_NAME"
         echo "Skipping - assuming installed kernel is OK."