post_process: fix pylint W1732,W1705,W1722

Fix pylint findings:
- R1732 consider-using-with
- R1705 no-else-return
- R1722 consider-using-sys-exit

Signed-off-by: Pawel Piatek <pawelx.piatek@intel.com>
Change-Id: If409c34f2ab8712e3fb1ac25b1c297d7e75c38fb
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/12139
Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>

autorun_post.py

@@ -4,6 +4,7 @@ import shutil
 import subprocess
 import argparse
 import os
+import sys
 import glob
 import re
 import pandas as pd
@@ -73,10 +74,11 @@ def generateCoverageReport(output_dir, repo_dir):
         print("lcov failed")
         print(e)
         return
-    cov_total_file = open(cov_total, 'r')
-    replacement = "SF:" + repo_dir
+
+    with open(cov_total, 'r') as cov_total_file:
         file_contents = cov_total_file.readlines()
-    cov_total_file.close()
+
+    replacement = "SF:" + repo_dir
     os.remove(cov_total)
     with open(cov_total, 'w+') as file:
         for Line in file_contents:
@@ -144,7 +146,7 @@ def getSkippedTests(repo_dir):
     skipped_test_file = os.path.join(repo_dir, "test", "common", "skipped_tests.txt")
     if not os.path.exists(skipped_test_file):
         return []
-    else:
+
     with open(skipped_test_file, "r") as skipped_test_data:
         return [x.strip() for x in skipped_test_data.readlines() if "#" not in x and x.strip() != '']
 
@@ -155,7 +157,7 @@ def confirmPerPatchTests(test_list, skiplist):
     if len(missing_tests) > 0:
         print("Not all tests were run. Failing the build.")
         print(missing_tests)
-        exit(1)
+        sys.exit(1)
 
 
 def aggregateCompletedTests(output_dir, repo_dir, skip_confirm=False):
@@ -189,6 +191,8 @@ def aggregateCompletedTests(output_dir, repo_dir, skip_confirm=False):
     if not skip_confirm:
         confirmPerPatchTests(test_list, skipped_tests)
 
+    return 0
+
 
 def main(output_dir, repo_dir, skip_confirm=False):
     print("-----Begin Post Process Script------")