If TFTPDIR does not begin with /, correct it

TFTPDIR could be set without a leading /.  Support
this syntax by putting a slash in front and hoping
for the best

xCAT-server/share/xcat/install/scripts/post.xcat

@@ -19,6 +19,9 @@ if [ -z "$TFTPDIR" ]; then
 
     TFTPDIR="/tftpboot"
 fi
+if [[ $TFTPDIR != /* ]]; then
+    TFTPDIR="/"$TFTPDIR
+fi
 
 cd /tmp
 RAND=$(perl -e 'print int(rand(50)). "\n"')