Use proper c3p0 class

We've been getting warnings with C3P0.

WARN
org.hibernate.service.jdbc.connections.internal.ConnectionProviderInitiator -
HHH000208: org.hibernate.connection.C3P0ConnectionProvider has been deprecated
in favor of
org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider; that
provider will be used instead.
Merge pull request #722 from candlepin/c3p0

Use proper c3p0 class