Use ovs-vsctl commands to determine if the bridge exists instead of grep

Closes rcbops/chef-cookbooks#752
Merge pull request #104 from rackerjoe/Issue752

Merged automatically by jenkins after successful build test
template sqlalchemy_pool_size in ovs plugin conf

adds ["neutron"]["database"]["sqlalchemy_pool_size"] attribute that
defaults to 5.

Fixes rcbops/chef-cookbooks#755