Write input in json file

Write input in json file instead of preparing a separate input file.

Overlap/Tests/Input/successive_overlap_in.txt

- &MAIN_NML k_test_1 = 1 /
-/
-/

Overlap/Tests/short_tests.json

@@ -47,8 +47,7 @@
         ]
     },
     {
-        "stdin_filename":
-	"$src_dir/Overlap/Tests/Input/successive_overlap_in.txt",
+        "input": "&MAIN_NML k_test_1 = 1 /\n/\n/\n",
         "description": "Overlap of a snapshot with itself.",
         "title": "Successive_overlap",
         "command":
@@ -58,8 +57,7 @@
         ]
     },
     {
-        "stdin_filename":
-	"$src_dir/Overlap/Tests/Input/successive_overlap_in.txt",
+        "input": "&MAIN_NML k_test_1 = 1 /\n/\n/\n",
         "description": "Same as Successive_overlap, but with larger domain: region 5 instead of region 4.",
         "title": "Successive_overlap_region_5_one_date",
         "command":