test: fix minor pylint warnings

This fixes a bunch of minor pylint warnings:
  * Drop unused imports.
  * Fix "inline-JSON" formatting.
  * Fix space before/after brackets.
  * Use `_` for unused variables.
  * Break overlong lines.
  * Mark unittest as `no-self-use` if applicable.
  * Drop spurious newline at end of file.

test/test_boot.py

@@ -1,6 +1,5 @@
 
 import subprocess
-import unittest
 from . import osbuildtest
 
 
@@ -9,21 +8,23 @@ class TestBoot(osbuildtest.TestCase):
         _, output_id = self.run_osbuild("test/pipelines/f30-boot.json")
 
         r = subprocess.run(["qemu-system-x86_64",
-            "-snapshot",
-            "-m", "1024",
-            "-M", "accel=kvm:hvf:tcg",
+                            "-snapshot",
+                            "-m", "1024",
+                            "-M", "accel=kvm:hvf:tcg",
 
-            # be silent
-            "-nographic",
-            "-monitor", "none",
-            "-serial", "none",
+                            # be silent
+                            "-nographic",
+                            "-monitor", "none",
+                            "-serial", "none",
 
-            # create /dev/vport0p1
-            "-chardev", "stdio,id=stdio",
-            "-device", "virtio-serial",
-            "-device", "virtserialport,chardev=stdio",
+                            # create /dev/vport0p1
+                            "-chardev", "stdio,id=stdio",
+                            "-device", "virtio-serial",
+                            "-device", "virtserialport,chardev=stdio",
 
-            f"{self.get_path_to_store(output_id)}/f30-boot.qcow2"
-        ], encoding="utf-8", stdout=subprocess.PIPE, check=True)
+                            f"{self.get_path_to_store(output_id)}/f30-boot.qcow2"],
+                           encoding="utf-8",
+                           stdout=subprocess.PIPE,
+                           check=True)
 
         self.assertEqual(r.stdout.strip(), "running")