tests: Pass --output-directory to vm() and boot()

The integration tests build into a per-test `--output-directory`, but
the verbs that consume the build (vm, boot) did not pass it, so they
recovered the build's configuration from the history in the config
directory. This breaks parallel tests, as they read the history file
from current global file (i.e. whichever build happened to finish last).

This is the tests/__init__.py half of the reverted commit da49fe9.
(That wasn't problematic.)

Author: martinpitt

tests/__init__.py

@@ -126,12 +126,13 @@ def boot(self, options: Sequence[str] = (), args: Sequence[str] = ()) -> Complet
                 "--register=no",
                 "--machine",
                 self.machine,
+                "--output-directory", self.output_dir,
                 *options,
             ],
             args,
             stdin=sys.stdin if sys.stdin.isatty() else None,
             check=False,
-        )
+        )  # fmt: skip
 
         if result.returncode != 123:
             raise subprocess.CalledProcessError(result.returncode, result.args, result.stdout, result.stderr)
@@ -158,12 +159,13 @@ def vm(
                 "--register=no",
                 "--machine",
                 self.machine,
+                "--output-directory", self.output_dir,
                 *options,
             ],
             args,
             stdin=sys.stdin if sys.stdin.isatty() else None,
             check=False,
-        )
+        )  # fmt: skip
 
         if result.returncode != 123:
             raise subprocess.CalledProcessError(result.returncode, result.args, result.stdout, result.stderr)