Do not default username/password for DataSource unless embedded

To use a DataSource pool (Tomcat or DBCP) the user must supply a valid
driver class name *and* database URL. If both are supplied and the
driver class is not one of the embedded ones, then no default username
or password is provided.

Fixes gh-94

spring-boot-dependencies/pom.xml

@@ -28,6 +28,7 @@
 		<log4j.version>1.2.17</log4j.version>
 		<logback.version>1.0.13</logback.version>
 		<mockito.version>1.9.5</mockito.version>
+		<mysql.version>5.1.23</mysql.version>
 		<reactor.version>1.0.0.M3</reactor.version>
 		<servlet-api.version>3.0.1</servlet-api.version>
 		<slf4j.version>1.7.5</slf4j.version>
@@ -104,6 +105,11 @@
 				<artifactId>log4j</artifactId>
 				<version>${log4j.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>mysql</groupId>
+				<artifactId>mysql-connector-java</artifactId>
+				<version>${mysql.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>nz.net.ultraq.thymeleaf</groupId>
 				<artifactId>thymeleaf-layout-dialect</artifactId>