core:DB upgrade from 3.0 to 3.1 fails

Fixing the general functions that creates/drops constraint to be
case-insensitive since entity names are case-insensitive in postgres
while values are case-sensitive.

Since the 03_01_1520_add_fk_vm_interface_vm_static_template.sql tries to
insert a new constraint named FK_vm_interface_vm_static_template while
in the database there was already a fk_vm_interface_vm_static_template
constraint install, there was an attempt to install this FK again which
failed.

The solution turns the '=' operation to 'ilike' when we look for an
existing constraint by its name.

Change-Id: Id36c83154559d6062609d08068989d3ce3d2c468
Signed-off-by: Eli Mesika <emesika@redhat.com>
Bug-Url:https://bugzilla.redhat.com/show_bug.cgi?id=892532