automount: fix handling of default dependencies for automount units

First After=local-fs-pre.target wasn't described in the man page although it's
part of the default dependencies automatically set by pid1.

Secondly, Before=local-fs.target was only set if the automount unit was
generated from the fstab-generator because the dep was explicitly
generated. It was also not documented as a default dependency.

Fix it by managing the dep from pid1 instead.

man/systemd.automount.xml

@@ -86,6 +86,10 @@
         <listitem><para>Automount units acquire automatic <varname>Before=</varname> and
         <varname>Conflicts=</varname> on <filename>umount.target</filename> in order to be stopped during
         shutdown.</para></listitem>
+
+        <listitem><para>Automount units automatically gain an <varname>After=</varname> dependency
+        on <filename>local-fs-pre.target</filename>, and a <varname>Before=</varname> dependency on
+        <filename>local-fs.target</filename>.</para></listitem>
       </itemizedlist>
     </refsect2>
   </refsect1>

src/core/automount.c

@@ -152,6 +152,10 @@ static int automount_add_default_dependencies(Automount *a) {
         if (!MANAGER_IS_SYSTEM(UNIT(a)->manager))
                 return 0;
 
+        r = unit_add_dependency_by_name(UNIT(a), UNIT_BEFORE, SPECIAL_LOCAL_FS_TARGET, true, UNIT_DEPENDENCY_DEFAULT);
+        if (r < 0)
+                return r;
+
         r = unit_add_dependency_by_name(UNIT(a), UNIT_AFTER, SPECIAL_LOCAL_FS_PRE_TARGET, true, UNIT_DEPENDENCY_DEFAULT);
         if (r < 0)
                 return r;

src/fstab-generator/fstab-generator.c

@@ -526,8 +526,6 @@ static int add_mount(
                         "Documentation=man:fstab(5) man:systemd-fstab-generator(8)\n",
                         source);
 
-                fprintf(f, "Before=%s\n", post);
-
                 if (opts) {
                         r = write_after(f, opts);
                         if (r < 0)