generate_test_[keys/cert_macros]: minor fixes

- remove new line at beginning of test_keys.h
- add footer at the end of both generated files

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/scripts/generate_test_cert_macros.py b/tests/scripts/generate_test_cert_macros.py
index 1472370..07c5b7d 100755
--- a/tests/scripts/generate_test_cert_macros.py
+++ b/tests/scripts/generate_test_cert_macros.py
@@ -72,7 +72,8 @@
     """
     template_loader = jinja2.FileSystemLoader(DATA_FILES_PATH)
     template_env = jinja2.Environment(
-        loader=template_loader, lstrip_blocks=True, trim_blocks=True)
+        loader=template_loader, lstrip_blocks=True, trim_blocks=True,
+        keep_trailing_newline=True)
 
     def read_as_c_array(filename):
         with open(filename, 'rb') as f:
diff --git a/tests/scripts/generate_test_keys.py b/tests/scripts/generate_test_keys.py
index 335e848..177850e 100755
--- a/tests/scripts/generate_test_keys.py
+++ b/tests/scripts/generate_test_keys.py
@@ -92,7 +92,7 @@
 
 def write_output_file(output_file_name: str, arrays: List[str], look_up_table: List[str]):
     with open(output_file_name, 'wt') as output:
-        output.write("""
+        output.write("""\
 /*********************************************************************************
  * This file was automatically generated from tests/scripts/generate_test_keys.py.
  * Please do not edit it manually.
@@ -112,6 +112,8 @@
 struct predefined_key_element predefined_keys[] = {{
 {}
 }};
+
+/* End of generated file */
 """.format("\n".join(look_up_table)))