Packaging: Check if proc file exists before calling sysctl

The packaged init scripts could return an error, if the file
/proc/sys/vm/max_map_count was not existing and we still called
sysctl.

This is primarly to prevent confusing error messages when elasticsearch
is started under virtualized environments without a proc file system.

Closes #4978

src/deb/init.d/elasticsearch

@@ -157,7 +157,7 @@ case "$1" in
 		ulimit -l $MAX_LOCKED_MEMORY
 	fi
 
-	if [ -n "$MAX_MAP_COUNT" ]; then
+	if [ -n "$MAX_MAP_COUNT" -a -f /proc/sys/vm/max_map_count ]; then
 		sysctl -q -w vm.max_map_count=$MAX_MAP_COUNT
 	fi
 

src/rpm/init.d/elasticsearch

@@ -77,7 +77,7 @@ start() {
     if [ -n "$MAX_LOCKED_MEMORY" ]; then
         ulimit -l $MAX_LOCKED_MEMORY
     fi
-    if [ -n "$MAX_MAP_COUNT" ]; then
+    if [ -n "$MAX_MAP_COUNT" -a -f /proc/sys/vm/max_map_count ]; then
         sysctl -q -w vm.max_map_count=$MAX_MAP_COUNT
     fi
     if [ -n "$WORK_DIR" ]; then