Add isort check for changed files

After discussing with pstodulk a massive change introducing isort
rules and fixing all occurrencies may be too annoying, so let's
make it gradually - intoduce a handmade isort check for changed files
only.
This patch also introduces a lint_fix target that can do fix the order
inplace automatically.

.isort.cfg

@@ -0,0 +1,9 @@
+[settings]
+line_length=119
+known_first_party=leapp
+multi_line_output=3
+honor_noqa=true
+# NOTE(ivasilev) Ideal solution would be order_by_type with classes exception (for ex. RPM) but this isn't supported
+# in 4.3.2
+case_sensitive=false
+order_by_type=false

Makefile

@@ -106,6 +106,7 @@ help:
 	@echo "  install-deps-fedora    create python virtualenv and install there"
 	@echo "                         leapp-repository with dependencies for Fedora OS"
 	@echo "  lint                   lint source code"
+	@echo "  lint_fix               attempt to fix isort violations inplace"
 	@echo "  test                   lint source code and run tests"
 	@echo "  test_no_lint           run tests without linting the source code"
 	@echo ""
@@ -260,6 +261,21 @@ lint:
 		echo "--- Linting done. ---"; \
 	fi
 
+	. $(VENVNAME)/bin/activate; \
+	git diff $(MASTER_BRANCH) --name-only | xargs isort -c --diff || \
+	{ \
+		echo; \
+		echo "------------------------------------------------------------------------------"; \
+		echo "Hint: Apply the required changes."; \
+		echo "      Execute the following command to apply them automatically: make lint_fix"; \
+		exit 1; \
+	} && echo "--- isort check done. ---";
+
+lint_fix:
+	. $(VENVNAME)/bin/activate; \
+	git diff $(MASTER_BRANCH) --name-only | xargs isort && \
+	echo "--- isort inplace fixing done. ---;"
+
 test_no_lint:
 	. $(VENVNAME)/bin/activate; \
 	snactor repo find --path repos/; \

requirements.txt

@@ -1,7 +1,7 @@
 ### Additional requirements
 
 flake8
-flake8-import-order
+isort
 funcsigs==1.0.2
 mock==2.0.0
 pylint