Clarify that schedule config's startTime hour must be zero-padded

Configuring a startTime as "6:00" is incorrect; it should be "06:00".

Clarify this in the documentation and fix the Javadoc that shows an
incorrect value. Also add a test.

Change-Id: I8e72d42088163b6659204913e8b0685bd957c3d8

Documentation/config-gerrit.txt

@@ -5064,7 +5064,7 @@ The placeholders can have the following values:
 
 +
 The time zone cannot be specified but is always the system default
-time zone.
+time zone. Hours must be zero-padded, i.e. `06:00` rather than `6:00`.
 
 The section (and optionally the subsection) in which the `interval` and
 `startTime` keys must be set depends on the background job for which a

java/com/google/gerrit/server/config/ScheduleConfig.java

@@ -91,7 +91,7 @@ import org.eclipse.jgit.lib.Config;
  *       executions are {@code Wed 10:30}, {@code Fri 10:30}. etc.
  *   <li>
  *       <pre>
- * foo.startTime = 6:00
+ * foo.startTime = 06:00
  * foo.interval = 1 day
  * </pre>
  *       Assuming that the server is started on {@code Mon 7:00} then this yields the first run on

javatests/com/google/gerrit/server/config/ScheduleConfigTest.java

@@ -202,6 +202,9 @@ public class ScheduleConfigTest {
 
     rc.setString("a", null, ScheduleConfig.KEY_STARTTIME, "0100");
     assertThat(ScheduleConfig.builder(rc, "a").buildSchedule()).isEmpty();
+
+    rc.setString("a", null, ScheduleConfig.KEY_STARTTIME, "1:00");
+    assertThat(ScheduleConfig.builder(rc, "a").buildSchedule()).isEmpty();
   }
 
   @Test