tests: run 'device-crash-test' from tests/venv

Remove the sys.path hacking from device-crash-test, and add in a little
user-friendly message for anyone who was used to running this script
directly from the source tree.

Modify the GitLab job recipes to create the tests/venv first, then run
device-crash-test from that venv.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220526000921.1581503-10-jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

.gitlab-ci.d/buildtest.yml

@@ -110,7 +110,8 @@ crash-test-debian:
     IMAGE: debian-amd64
   script:
     - cd build
-    - scripts/device-crash-test -q ./qemu-system-i386
+    - make check-venv
+    - tests/venv/bin/python3 scripts/device-crash-test -q ./qemu-system-i386
 
 build-system-fedora:
   extends: .native_build_job_template
@@ -155,8 +156,9 @@ crash-test-fedora:
     IMAGE: fedora
   script:
     - cd build
-    - scripts/device-crash-test -q ./qemu-system-ppc
-    - scripts/device-crash-test -q ./qemu-system-riscv32
+    - make check-venv
+    - tests/venv/bin/python3 scripts/device-crash-test -q ./qemu-system-ppc
+    - tests/venv/bin/python3 scripts/device-crash-test -q ./qemu-system-riscv32
 
 build-system-centos:
   extends: .native_build_job_template

scripts/device-crash-test

@@ -33,10 +33,18 @@ import re
 import random
 import argparse
 from itertools import chain
-
-sys.path.append(os.path.join(os.path.dirname(__file__), '..', 'python'))
-from qemu.machine import QEMUMachine
-from qemu.qmp import ConnectError
+from pathlib import Path
+
+try:
+    from qemu.machine import QEMUMachine
+    from qemu.qmp import ConnectError
+except ModuleNotFoundError as exc:
+    path = Path(__file__).resolve()
+    print(f"Module '{exc.name}' not found.")
+    print("  Try 'make check-venv' from your build directory,")
+    print("  and then one way to run this script is like so:")
+    print(f'  > $builddir/tests/venv/bin/python3 "{path}"')
+    sys.exit(1)
 
 logger = logging.getLogger('device-crash-test')
 dbg = logger.debug