Add BUILDER_WEB_DATADIR env, fix bug

The builder-web commands now understand the BUILDER_WEB_DATADIR
environment variable which is used as --datadir.

During a change the transaction when vacuuming was committed twice which
is an error in sqlite. This was found during testing.

bin/builder_db_app.ml

@@ -244,7 +244,6 @@ let vacuum datadir (module Db : Caqti_blocking.CONNECTION) platform_opt job_id p
        this is too verbose? *)
     Logs.info (fun m -> m "Job %s %a; not removing any builds"
                   jobname pp_reason predicate);
-  let* () =
   List.fold_left (fun r (build_id, build) ->
       let* () = r in
       let* () = Db.start () in
@@ -259,8 +258,6 @@ let vacuum datadir (module Db : Caqti_blocking.CONNECTION) platform_opt job_id p
         e)
     (Ok ())
     builds
-  in
-  Db.commit ()
 
 let vacuum () datadir platform_opt jobnames predicate =
   let dbpath = datadir ^ "/builder.sqlite3" in
@@ -838,15 +835,17 @@ let dbpath_new =
 
 let datadir =
   let doc = "Data directory." in
+  let env = Cmdliner.Cmd.Env.info "BUILDER_WEB_DATADIR" in
   Cmdliner.Arg.(value &
                 opt dir Builder_system.default_datadir &
-                info ~doc ["datadir"; "d"])
+                info ~doc ~env ["datadir"; "d"])
 
 let cachedir =
   let doc = "Cache directory." in
+  let env = Cmdliner.Cmd.Env.info "BUILDER_WEB_CACHEDIR" in
   Cmdliner.Arg.(value &
                 opt (some dir) None &
-                info ~doc ["cachedir"])
+                info ~doc ~env ["cachedir"])
 
 let jobname =
   let doc = "Jobname." in

bin/builder_web_app.ml

@@ -196,10 +196,11 @@ let ip_port : (Ipaddr.V4.t * int) Arg.conv =
 let datadir =
   let doc = "data directory" in
   let docv = "DATA_DIR" in
+  let env = Cmdliner.Cmd.Env.info "BUILDER_WEB_DATADIR" in
   Arg.(
     value &
     opt dir Builder_system.default_datadir &
-    info [ "d"; "datadir" ] ~doc ~docv
+    info ~env [ "d"; "datadir" ] ~doc ~docv
   )
 
 let cachedir =

bin/migrations/builder_migrations.ml

@@ -61,9 +61,10 @@ let help man_format migrations = function
 
 let datadir =
   let doc = "data directory containing builder.sqlite3 and data files" in
+  let env = Cmdliner.Cmd.Env.info "BUILDER_WEB_DATADIR" in
   Cmdliner.Arg.(value &
                 opt dir Builder_system.default_datadir &
-                info ~doc ["datadir"; "d"])
+                info ~env ~doc ["datadir"; "d"])
 
 let setup_log =
   let setup_log level =