Make tests return the number of errors as exit code.

scripts/run-tests-e3.lua

@@ -16,4 +16,5 @@ require 'lunit'
 
 eressea.settings.set("rules.alliances", "0")
 rules = require('eressea.' .. config.rules)
-lunit.main()
+result = lunit.main()
+return result.errors

scripts/run-tests.lua

@@ -10,4 +10,5 @@ require 'eressea'
 require 'eressea.path'
 require 'tests'
 require 'lunit'
-lunit.main()
+result = lunit.main()
+return result.errors