Added preamble feature to host test.
Added preamble feature to host test.

Test cases will print something like this to inform user this is automated test
case:

{{timeout;20}}
{{host_test_name;default_auto}}
{{description;Basic}}
{{test_id;MBED_A1}}
+--------------------------------------------------------------------------+
+ This test case is meant to be executed in an automated test environment. +
+ It will fail if used without the test suite instrumentation.             +
+--------------------------------------------------------------------------+
{{start}}
{{success}}
{{end}}

iriark01/htrun,iriark01/htrun