Use lf-activate-venv for Robot virtual environment

The virtual environment for Robot Framework is created with the system
default Python 3.6 which is not supported any more.

Use lf-activate-venv instead to leverage more recent version of Python
and change the shell back to bash since 'lf-env.sh' is not POSIX
compliant.

Remove odltools from the requirements since odltools CSIT jobs have been
removed.

Change-Id: I62f9d580b77a877572a78730d43b99e6c419d215
Signed-off-by: Sangwook Ha <sangwook.ha@verizon.com>