If you modify the context.xml at Tomcat level ($CATALINA_BASE/conf/context.xml), then you do not need to modify gwt-console-server's context.xml.
Modify the context.xml in Tomcat's conf directory
<Transaction factory="bitronix.tm.BitronixUserTransactionObjectFactory" />
<Resource name="jdbc/testDS1" auth="Container" type="javax.sql.DataSource"
maxActive="15" maxIdle="2" maxWait="10000"
logAbandoned="true"
username="testing" password=""
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost/jbpm"/>
If you define the username etc in context.xml, you can delete them from resources.properties.
Make sure if you include mysql jar file in Tomcat's lib directory