Support multiple hosts for PostgreSQL and MySQL

[pivotal-david-osullivan]

Addresses #128

java.net.URI cannot parse a multi-host authority such as
jdbc:postgresql://host1:port1,host2:port2/database — it falls back to
registry-based parsing, where getHost() returns null and getPort()
returns -1, even though getAuthority() still holds the full value.

Changes

• UriInfo now detects that fallback and, when the authority contains a
  comma, parses the host list manually. getHost()/getPort() keep
  returning the first host for backwards compatibility, and a new
  getHostAndPort() accessor exposes the full list.
• Parsing uses getRawAuthority() rather than the percent-decoded
  getAuthority(), so a password containing an encoded :, , or @
  is not mistaken for a delimiter. Decoding happens after splitting,
  matching the existing parseUserinfo() behaviour.
• PostgresqlJdbcUrlCreator uses getHostAndPort() so every host
  survives into the generated JDBC URL.
• MySqlJdbcUrlCreator does the same. MySQL and MariaDB support the same
  host1,host2 failover syntax, and it shares the UriInfo code path, so
  without this it would have silently emitted a first-host-only URL.
• Authorities that fail server-based parsing without containing a comma
  (for example SQL Server’s ;property=value suffix) keep their previous
  behaviour and continue to be handled by their own creator.

Tests

• UriInfoTests: multi-host with and without userinfo, a percent-encoded
  : in the password, a non-PostgreSQL (mysql) multi-host authority, and
  a single-host case asserting the standard path is unaffected.
• PostgresqlJdbcTests / MySqlJdbcTests: end-to-end VCAP_SERVICES
  payloads asserting all hosts reach the JDBC URL.

[kvmw]

LGTM