Set database pool_size in ironic.conf and inspector.conf templates

Set database pool_size in ironic.conf and inspector.conf templates

min_pool_size and max_pool_size are undefined in ironic.conf and inspector.conf
templates, causing issues during ironic-dbsync and ironic-inspector-dbsync.

https://build.opnfv.org/ci/job/opnfv-bifrost-verify-trusty-virtual-master/224/console

This issue is there for stable/ocata as well.

These should be got rid of once the patch on openstack/bifrost is merged.
https://review.openstack.org/#/c/450681/

Change-Id: I678835e763022a7168e498047bb65d140895e019
Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>