Add system's requirements.txt, enforce flake8 linter

Fix style issues in functional tests.

system/t04_mirror/search.py

@@ -1,12 +1,16 @@
 from lib import BaseTest
 
 
+def sortLines(_, s):
+    return "\n".join(sorted(s.split("\n")))
+
+
 class SearchMirror1Test(BaseTest):
     """
     search mirror: regular search
     """
     fixtureDB = True
-    outputMatchPrepare = lambda _, s: "\n".join(sorted(s.split("\n")))
+    outputMatchPrepare = sortLines
     runCmd = "aptly mirror search wheezy-main '$$Architecture (i386), Name (% *-dev)'"
 
 
@@ -32,7 +36,7 @@ class SearchMirror4Test(BaseTest):
     search mirror: with-deps search
     """
     fixtureDB = True
-    outputMatchPrepare = lambda _, s: "\n".join(sorted(s.split("\n")))
+    outputMatchPrepare = sortLines
     runCmd = "aptly mirror search -with-deps wheezy-main 'Name (nginx)'"
 
 
@@ -41,7 +45,7 @@ class SearchMirror5Test(BaseTest):
     search mirror: regular search
     """
     fixtureDB = True
-    outputMatchPrepare = lambda _, s: "\n".join(sorted(s.split("\n")))
+    outputMatchPrepare = sortLines
     runCmd = "aptly mirror search -format='{{.Package}}#{{.Version}}' wheezy-main '$$Architecture (i386), Name (% *-dev)'"
 
 
@@ -50,5 +54,5 @@ class SearchMirror6Test(BaseTest):
     search mirror: no query
     """
     fixtureDB = True
-    outputMatchPrepare = lambda _, s: "\n".join(sorted(s.split("\n")))
+    outputMatchPrepare = sortLines
     runCmd = "aptly mirror search -format='{{.Package}}#{{.Version}}' wheezy-main"