assemblers: use api.arguments

Instead of reading the arguments from sys.stdin, which requires
that stdin is setup properly for that in the runner, use the new
api.arguments() method to directly fetch the arguments.

Also fix missing newlines between imports and methods to be more
PEP-8 complaint, where needed.

assemblers/org.osbuild.rawfs

@@ -21,12 +21,14 @@ read from `/proc/sys/kernel/random/uuid` if your kernel provides it.
 
 
 import contextlib
-import json
 import os
 import subprocess
 import sys
+
+import osbuild.api
 import osbuild.remoteloop as remoteloop
 
+
 SCHEMA = """
 "additionalProperties": false,
 "required": ["filename", "root_fs_uuid", "size"],
@@ -104,6 +106,6 @@ def main(tree, output_dir, options, loop_client):
 
 
 if __name__ == '__main__':
-    args = json.load(sys.stdin)
+    args = osbuild.api.arguments()
     r = main(args["tree"], args["output_dir"], args["options"], remoteloop.LoopClient("/run/osbuild/api/remoteloop"))
     sys.exit(r)