Shortened tablenames constants in Neutron driver

Previously, the constants for tablenames in the Neutron
driver were all prefixed with NEUTRON_, e.g.
NEUTRON_PORTS_SECURITY_GROUPS.  This prefix is unnecessary
since it is clear from context.

This change removes the prefix throughout the codebase.

Change-Id: Ib9cea8243886523ad639f7151ac593fc3ad21804
Merge "Shortened tablenames constants in Neutron driver"