Integrated a module that retains an RSA key pair as an identity.

This is a proof of concept to core modulizarion (by binary integration.)
A module is built like a plugin but it's packaged to the war as a
WEB-INF/lib/*.jar, not as a plugin.

Compared to plugins, jars integrated in this way do not double-package
dependency jars, and they are not visible to the users. I plan to try a
few of these and if it's useful, this could be an useful mechanism for
modularizing core.

war/pom.xml

@@ -258,6 +258,12 @@ THE SOFTWARE.
       <version>${project.version}</version>
       <scope>provided</scope>
     </dependency>
+    <dependency>
+      <groupId>org.jenkins-ci.modules</groupId>
+      <artifactId>instance-identity</artifactId>
+      <version>1.0</version>
+    </dependency>
+
     <!-- offline profiler API when we need it -->
     <!--dependency>
       <groupId>com.yourkit.api</groupId>