Low: mysql pgsql: Using crm_node -n for instance attributes instead of uname -n

There are use cases where it is possible to have cluster node
names that are not the same as what is returned by uname -n. We
need to be using whatever crm_node -n returns as our local cluster
node name when setting node attributes rather than uname -n.

Switching to 'crm_node -n' from 'uname -n' only needs to happen
for pacemaker versions greater than 1.1.8.