Add/use watchdog with standard timeout

Almost all uses of the watchdog use the same 500ms timeout, so add a new
method that assumes that.

Test: CtsKeystoreTestCases
Change-Id: Idf7852400a58ba954e4a71e5e2282734a0960072
diff --git a/keystore2/src/watchdog_helper.rs b/keystore2/src/watchdog_helper.rs
index 92a0abc..03c7740 100644
--- a/keystore2/src/watchdog_helper.rs
+++ b/keystore2/src/watchdog_helper.rs
@@ -23,6 +23,11 @@
     pub use watchdog_rs::WatchPoint;
     use watchdog_rs::Watchdog;
 
+    /// Default timeout interval, in milliseconds.
+    pub const DEFAULT_TIMEOUT_MS: u64 = 500;
+
+    const DEFAULT_TIMEOUT: Duration = Duration::from_millis(DEFAULT_TIMEOUT_MS);
+
     lazy_static! {
         /// A Watchdog thread, that can be used to create watch points.
         static ref WD: Arc<Watchdog> = Watchdog::new(Duration::from_secs(10));
@@ -33,6 +38,11 @@
         Watchdog::watch(&WD, id, Duration::from_millis(millis))
     }
 
+    /// Sets a watch point with `id` and a default timeout of [`DEFAULT_TIMEOUT_MS`] milliseconds.
+    pub fn watch(id: &'static str) -> Option<WatchPoint> {
+        Watchdog::watch(&WD, id, DEFAULT_TIMEOUT)
+    }
+
     /// Like `watch_millis` but with a callback that is called every time a report
     /// is printed about this watch point.
     pub fn watch_millis_with(
@@ -53,6 +63,10 @@
     fn watch_millis(_: &'static str, _: u64) -> Option<WatchPoint> {
         None
     }
+    /// Sets a Noop watch point.
+    fn watch(_: &'static str) -> Option<WatchPoint> {
+        None
+    }
 
     pub fn watch_millis_with(
         _: &'static str,