test/py: add timestamps to log

It can be useful to record how long tests take; this can help debug slow
running test systems or track changes in performance over time. Enhance
the test system to record timestamps while running test:
- Whenever a new log file section is started.
- After U-Boot is started and communication has been established.
- After each host or U-Boot command is executed.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

test/py/u_boot_console_base.py

@@ -215,6 +215,8 @@ class ConsoleBase(object):
             self.log.error(str(ex))
             self.cleanup_spawn()
             raise
+        finally:
+            self.log.timestamp()
 
     def run_command_list(self, cmds):
         """Run a list of commands.
@@ -370,6 +372,7 @@ class ConsoleBase(object):
             self.cleanup_spawn()
             raise
         finally:
+            self.log.timestamp()
             self.log.end_section('Starting U-Boot')
 
     def cleanup_spawn(self):