You have <max-pool-size> at 1 - it doesn't matter how many the connections the database is configured for.
Your log shows that the app gives up after 30 seconds to get a connection, which is default.
Your prefill at true doesn't do anything, since your <min-pool-size> is 0.
http://docs.jboss.org/ironjacamar/userguide/1.0/en-US/html/deployment.html#deployingds_descriptor