Add timestamp and phase entry and exit prints to build log.

When testscript.pm now enters a new job or phase, it will print to
log a timestamped entry. This will also be printed with duration
at the point of exit.
example of entry and exit:
09:34:21 #=# Wed Apr 17 09:34:21 2013 #=# >cleaning existing target directories
09:34:36 #=# Wed Apr 17 09:34:36 2013 #=# <cleaning existing target directories #=# Elapsed 15 second(s).

Change-Id: I76a300244ea09193f877f57c3ed1f9e44a4b3d2b
Reviewed-by: Janne Anttila <janne.anttila@digia.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>