OUT ON SET DEBUG_SYNC

Issue:
------
SET DEBUG_SYNC = 'now WAIT_FOR something' statement in a test cases
test time out, because something is never triggered, then the most
recent '--echo' command is not reflected in the log file.

bash> echo sample.test
--echo one
--echo two
--echo three
SET DEBUG_SYNC = 'now WAIT_FOR ever';

bash> ./mtr main.sample --testcase-timeout=1

This obviously will timeout, since we never trigger signal named
'ever'. But, the strange thing is that log file contains only:

bash> cat var/log/main.sample/sample.log
one
two

The last echo statement output is not written to the log file.

Fix:
----
1. Flush the the contents in output buffer to file after writing the
   them.

2. Created 'include/analyze-timeout.test' file.

Change-Id: Id5449a3893958123a1ed555e57ed757643200abd