The image creates SWW_STATE_DIR when it is missing (closes #337)

Before waf starts, share/sww.run makes SWW_STATE_DIR if it is missing,
gives it to sww:sww and sets its mode to 0700. A setting that is not an
absolute path, or a SWW_STATE_DIR_FILE that cannot be read, still
changes nothing. script/example-app now checks that a waf container
whose SWW_STATE_DIR does not exist becomes healthy with the directory
made for sww, mode 0700.

Model: opus-5-5

Dockerfile

@@ -222,8 +222,8 @@ RUN groupadd --system --gid 65532 sww \
         sww
 
 # The state files' directory, SWW_STATE_DIR by default, where a volume
-# is mounted to keep them across deploys. The run script gives it to the
-# sww user at each start of waf.
+# is mounted to keep them across deploys. At each start of waf, the run
+# script makes SWW_STATE_DIR if it is missing and gives it to the sww user.
 RUN mkdir /var/lib/sww
 
 # The default rule file, in SWW_RULES_DIR by default, where a Dockerfile