Fixed lp:886484 "nowatch option for mysqld (allow systemd)"

Added a --nowatch (with aliases --no-watch and --no-auto-restart) option to mysqld_safe that causes it to exit after
spawning mysqld.  We don't need mysqld_safe to restart mysqld after a crash, because systemd can do that just fine.

Based on code from Maarten Vanraes

scripts/mysqld_safe.sh:
  Added option --nowatch (with aliases --no-watch and --no-auto-restart)

scripts/mysqld_safe.sh

@@ -15,6 +15,7 @@
 KILL_MYSQLD=1;
 MYSQLD=
 niceness=0
+nowatch=0
 mysqld_ld_preload=
 mysqld_ld_library_path=
 
@@ -44,16 +45,18 @@ usage () {
         cat <<EOF
 Usage: $0 [OPTIONS]
   --no-defaults              Don't read the system defaults file
+  --core-file-size=LIMIT     Limit core files to the specified size
   --defaults-file=FILE       Use the specified defaults file
   --defaults-extra-file=FILE Also use defaults from the specified file
   --ledir=DIRECTORY          Look for mysqld in the specified directory
   --open-files-limit=LIMIT   Limit the number of open files
-  --core-file-size=LIMIT     Limit core files to the specified size
   --timezone=TZ              Set the system timezone
   --malloc-lib=LIB           Preload shared library LIB if available
   --mysqld=FILE              Use the specified file as mysqld
   --mysqld-version=VERSION   Use "mysqld-VERSION" as mysqld
   --nice=NICE                Set the scheduling priority of mysqld
+  --no-auto-restart          Exit after starting mysqld
+  --nowatch                  Exit after starting mysqld
   --plugin-dir=DIR           Plugins are under DIR or DIR/VERSION, if
                              VERSION is given
   --skip-kill-mysqld         Don't try to kill stray mysqld processes
@@ -140,8 +143,16 @@ eval_log_error () {
       ;;
   esac
 
-  #echo "Running mysqld: [$cmd]"
-  eval "$cmd"
+  if test $nowatch -eq 1
+  then
+    # We'd prefer to exec $cmd here, but SELinux needs to be fixed first
+    #/usr/bin/logger "Running mysqld: $cmd"
+    eval "$cmd &"
+    exit 0
+  else
+    #echo "Running mysqld: [$cmd]"
+    eval "$cmd"
+  fi
 }
 
 shell_quote_string() {
@@ -202,6 +213,7 @@ parse_arguments() {
         fi
         ;;
       --nice=*) niceness="$val" ;;
+      --nowatch|--no-watch|--no-auto-restart) nowatch=1 ;;
       --open-files-limit=*) open_files="$val" ;;
       --open_files_limit=*) open_files="$val" ;;
       --skip-kill-mysqld*) KILL_MYSQLD=0 ;;