image-tests: fix hostname typo in customizations

The test case generation script contained a typo in the blueprint
customizations dictionary: "hosname" instead of "hostname".

Fixed typo and regenerated relevant test cases.

tools/test-case-generators/generate-test-cases

@@ -109,7 +109,7 @@ CUSTOMIZATIONS_BLUEPRINT =  {
         }
     ],
     "customizations": {
-        "hosname": "my-host",
+        "hostname": "my-host",
         "kernel": {
             "append": "debug"
         },