test_cli: workaround pytest log indentation behaviour change

pytest 4.6.x started indenting trailing lines in log messages, which
meant that our matching in the affected test stopped working once we
introduced newlines into the relevant log output in canonical#973.

If focal moves onto pytest 5.x before release, then we can remove this
workaround.

The upstream issue is pytest-dev/pytest#5515

uaclient/tests/test_cli.py

@@ -289,6 +289,14 @@ def test_user_facing_error_handled_gracefully(
         assert "" == out
         assert "{}\n".format(expected_msg) == err
         error_log = caplog_text()
+        # pytest 4.6.x started indenting trailing lines in log messages, which
+        # meant that our matching here stopped working once we introduced
+        # newlines into this log output in #973.  (If focal moves onto pytest
+        # 5.x before release, then we can remove this workaround.)  The
+        # upstream issue is https://github.com/pytest-dev/pytest/issues/5515
+        error_log = "\n".join(
+            [line.strip() for line in error_log.splitlines()]
+        )
         assert expected_msg in error_log
         assert "Traceback (most recent call last):" in error_log