refactor(postscripts): share RPM package manager discovery

Signed-off-by: Vinícius Ferrão <2031761+viniciusferrao@users.noreply.github.com>

xCAT/postscripts/ospkgs

@@ -910,11 +910,7 @@ elif ( pmatch "$OSVER" "ubuntu*" ); then
 	fi
 else
     #check if yum or dnf is installed
-    if [ -x /usr/bin/dnf ]; then
-	yumcmd="dnf"
-    elif [ -x /usr/bin/yum ]; then
-	yumcmd="yum"
-    else
+    if ! yumcmd=$(xcat_find_rpm_package_manager); then
 	echo "Please install yum or dnf on $NODE."
 	exit 1;
     fi

xCAT/postscripts/otherpkgs

@@ -509,12 +509,8 @@ else
     result=`rpm --version 2>/dev/null`
     if [ $? -eq 0 ]; then
          hasrpm=1
-         if [ -x /usr/bin/dnf ]; then
+         if yumcmd=$(xcat_find_rpm_package_manager); then
               hasyum=1
-              yumcmd="dnf"
-         elif [ -x /usr/bin/yum ]; then
-              hasyum=1
-              yumcmd="yum"
          else
               result=`rpm -q zypper`
               if [ "$?" = "0" ]; then

xCAT/postscripts/xcatpkgutils.sh

@@ -2,6 +2,18 @@
 # EPL license http://www.eclipse.org/legal/epl-v10.html
 
 # Shared POSIX shell helpers for the ospkgs and otherpkgs postscripts.
+
+xcat_find_rpm_package_manager()
+{
+    if [ -x "${1:-/usr/bin}/dnf" ]; then
+        printf '%s\n' dnf
+    elif [ -x "${1:-/usr/bin}/yum" ]; then
+        printf '%s\n' yum
+    else
+        return 1
+    fi
+}
+
 # Keep the marker assignment last so callers know the whole library loaded.
 # shellcheck disable=SC2034
 XCATPKGUTILS_LOADED=1