Fail builds on warnings
Fail builds on warnings

Also remove the unnecessary echo statement. Sphinx already prints a
message to indicate where the docs are at the end of the build so is
redundant and the echo fails Windows builders.

Change-Id: I16814a68230e5d37ffc351938e233c08499d240a
Signed-off-by: Thanh Ha <09ea4d3a79c8bee41a16519f6a431f6bc0fd8d6f@linuxfoundation.org>

opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt,opendaylight/netvirt