Dev: doc/man: Clean up ShellCheck warnings

In ./doc/man/mkappendix.sh line 10:
for manpage in `printf "%s\n" $@ | sort -f`; do
               ^-- SC2006: Use $(..) instead of legacy `..`.
                              ^-- SC2068: Double quote array expansions to avoid re-splitting elements.

In ./doc/man/ralist.sh line 7:
for f in `find $RADIR -type f -executable`; do
         ^-- SC2044: For loops over find output are fragile. Use find -exec or a while read loop.
         ^-- SC2006: Use $(..) instead of legacy `..`.
               ^-- SC2086: Double quote to prevent globbing and word splitting.

doc/man/mkappendix.sh

@@ -7,7 +7,7 @@ cat <<EOF
   <title>Resource agent manual pages</title>
 EOF
 
-for manpage in `printf "%s\n" $@ | sort -f`; do
+for manpage in $(printf "%s\n" "$@" | sort -f); do
     cat <<EOF
   <xi:include href="./$manpage" xmlns:xi="http://www.w3.org/2001/XInclude"/>
 EOF

doc/man/ralist.sh

@@ -4,6 +4,6 @@ RADIR=$1
 PREFIX=$2
 SUFFIX=$3
 
-for f in `find $RADIR -type f -executable`; do
-    echo ${PREFIX}`basename $f`${SUFFIX}
+find "$RADIR" -type f -executable | while read -r file; do
+    echo "${PREFIX}$(basename "$file")${SUFFIX}"
 done