map bool -> map struct{} (#2386)

This clear out the remaining map[x]bool usage and moves the bool to an
empty struct.

Two note worthy other changes:

* EnableChaos in the server is now also exported to make it show up in
  the documentation.
* The auto plugin is left as is, because there the boolean is
  explicitaly set to false to signal 'to-be-deleted' and the key is left
  as-is.

Signed-off-by: Miek Gieben <miek@miek.nl>

coremain/run.go

@@ -257,14 +257,14 @@ var (
 )
 
 // flagsBlacklist removes flags with these names from our flagset.
-var flagsBlacklist = map[string]bool{
-	"logtostderr":      true,
-	"alsologtostderr":  true,
-	"v":                true,
-	"stderrthreshold":  true,
-	"vmodule":          true,
-	"log_backtrace_at": true,
-	"log_dir":          true,
+var flagsBlacklist = map[string]struct{}{
+	"logtostderr":      struct{}{},
+	"alsologtostderr":  struct{}{},
+	"v":                struct{}{},
+	"stderrthreshold":  struct{}{},
+	"vmodule":          struct{}{},
+	"log_backtrace_at": struct{}{},
+	"log_dir":          struct{}{},
 }
 
 var flagsToKeep []*flag.Flag