test: fix pylint warning for capsule tests

Fix pylint warnings like:

* Class inherits from object
* Missing module description
* Missing class description
* First line of comment blank
* Superfluous imports

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/test/py/tests/test_efi_capsule/conftest.py b/test/py/tests/test_efi_capsule/conftest.py
index 4879f2b..0e5137d 100644
--- a/test/py/tests/test_efi_capsule/conftest.py
+++ b/test/py/tests/test_efi_capsule/conftest.py
@@ -2,30 +2,21 @@
 # Copyright (c) 2020, Linaro Limited
 # Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
 
-import os
-import os.path
-import re
-from subprocess import call, check_call, check_output, CalledProcessError
-import pytest
-from capsule_defs import *
+"""Fixture for UEFI capsule test
+"""
 
-#
-# Fixture for UEFI capsule test
-#
+from subprocess import call, check_call, CalledProcessError
+import pytest
+from capsule_defs import CAPSULE_DATA_DIR, CAPSULE_INSTALL_DIR, EFITOOLS_PATH
 
 @pytest.fixture(scope='session')
 def efi_capsule_data(request, u_boot_config):
-    """Set up a file system to be used in UEFI capsule and
-       authentication test.
+    """Set up a file system to be used in UEFI capsule and authentication test
+    and return a ath to disk image to be used for testing
 
-    Args:
-        request: Pytest request object.
-        u_boot_config: U-boot configuration.
-
-    Return:
-        A path to disk image to be used for testing
+    request -- Pytest request object.
+    u_boot_config -- U-boot configuration.
     """
-    global CAPSULE_DATA_DIR, CAPSULE_INSTALL_DIR
 
     mnt_point = u_boot_config.persistent_data_dir + '/test_efi_capsule'
     data_dir = mnt_point + CAPSULE_DATA_DIR