meson.build: more logging of the pytests

The terminal width pytest assumes is 80 chars wide so any errors during
fixtures are ellipsized and useless. Let pytest create an extra file
(shoving that into meson-logs because why not) and make it print a
summary, hopefully that makes it easier to narrow down errors.

meson.build

@@ -293,7 +293,13 @@ if get_option('tests').enabled()
 	pytest = find_program('pytest-3', 'pytest')
 	test('pytest',
 	     pytest,
-	     args: ['--verbose', '--log-level=DEBUG', meson.current_source_dir()],
+	     args: ['--verbose',
+		     '-rfES',
+		     '--log-level=DEBUG',
+		     '--log-file', meson.project_build_root() / 'meson-logs' / 'pytest.log',
+		     '--log-file-level=DEBUG',
+		     meson.current_source_dir()
+	     ],
 	     env: env,
 	     suite: ['all'])
 endif