Fix launching of test for 5.7 due to switch to java 7

17:18:42      [exec] stop-unix:
17:18:42      [exec]      [exec] Exception in thread "main" java.lang.UnsupportedClassVersionError: org/nuxeo/launcher/NuxeoLauncher : Unsupported major.minor version 51.0
17:18:42      [exec]      [exec] 	at java.lang.ClassLoader.defineClass1(Native Method)
17:18:42      [exec]      [exec] 	at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
17:18:42      [exec]      [exec] 	at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
17:18:42      [exec]      [exec] 	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
17:18:42      [exec]      [exec] 	at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
17:18:42      [exec]      [exec] 	at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
17:18:42      [exec]      [exec] 	at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
17:18:42      [exec]      [exec] 	at java.security.AccessController.doPrivileged(Native Method)
17:18:42      [exec]      [exec] 	at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
17:18:42      [exec]      [exec] 	at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
17:18:42      [exec]      [exec] 	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
17:18:42      [exec]      [exec] 	at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
17:18:42      [exec]      [exec] Could not find the main class: org.nuxeo.launcher.NuxeoLauncher. Program will exit.
17:18:42      [exec]      [exec] Result: 1