qapi: enforce import order/styling with isort

While we're mucking around with imports, we might as well formalize the
style we use. Let's use isort to do it for us.

lines_after_imports=2: Use two lines after imports, to match PEP8's
desire to have "two lines before and after" class definitions, which are
likely to start immediately after imports.

force_sort_within_sections: Intermingles "from x" and "import x" style
statements, such that sorting is always performed strictly on the module
name itself.

force_grid_wrap=4: Four or more imports from a single module will force
the one-per-line style that's more git-friendly. This will generally
happen for 'typing' imports.

multi_line_output=3: Uses the one-per-line indented style for long
imports.

include_trailing_comma: Adds a comma to the last import in a group,
which makes git conflicts nicer to deal with, generally.

line_length: 72 is chosen to match PEP8's "docstrings and comments" line
length limit. If you have a single line import that exceeds 72
characters, your names are too long!

Suggested-by: Cleber Rosa <crosa@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20201009161558.107041-8-jsnow@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/.isort.cfg

@@ -0,0 +1,7 @@
+[settings]
+force_grid_wrap=4
+force_sort_within_sections=True
+include_trailing_comma=True
+line_length=72
+lines_after_imports=2
+multi_line_output=3

scripts/qapi/expr.py

@@ -14,8 +14,9 @@
 # This work is licensed under the terms of the GNU GPL, version 2.
 # See the COPYING file in the top-level directory.
 
-import re
 from collections import OrderedDict
+import re
+
 from .common import c_name
 from .error import QAPISemError
 

scripts/qapi/introspect.py

@@ -17,8 +17,11 @@
     mcgen,
 )
 from .gen import QAPISchemaMonolithicCVisitor
-from .schema import (QAPISchemaArrayType, QAPISchemaBuiltinType,
-                     QAPISchemaType)
+from .schema import (
+    QAPISchemaArrayType,
+    QAPISchemaBuiltinType,
+    QAPISchemaType,
+)
 
 
 def _make_tree(obj, ifcond, features, extra=None):

scripts/qapi/parser.py

@@ -14,9 +14,9 @@
 # This work is licensed under the terms of the GNU GPL, version 2.
 # See the COPYING file in the top-level directory.
 
+from collections import OrderedDict
 import os
 import re
-from collections import OrderedDict
 
 from .error import QAPIParseError, QAPISemError
 from .source import QAPISourceInfo

scripts/qapi/schema.py

@@ -14,9 +14,9 @@
 
 # TODO catching name collisions in generated code would be nice
 
+from collections import OrderedDict
 import os
 import re
-from collections import OrderedDict
 
 from .common import c_name, pointer_suffix
 from .error import QAPIError, QAPISemError