Http Server: file length was missing in file API

File length was missing in the file API. This adds the missing attribute
and adds a test to verify all the attribute in the file API.

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
jvm_balloon: Add API to get the JVM balloon size

This adds an api with its own header file to return the balloon size.
Using a separate header file, removes the dependencies in other headers
such as JNI.

Reviewed-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>