[Profile] az login: Show warning for MFA error

[jiasli]

Partially mitigate #6962. MFA cross-tenant trust is still under development by service team.

During az login, show warning for MFA error. This happens when the home tenant doesn't require MFA but the other tenants where the user is a guest of do. When getting access token with refresh token for those MFA tenants, CLI gives the raw error which isn't very instructive:

AADSTS50076: Due to a configuration change made by your administrator, or because you moved to a new location, you must use multi-factor authentication to access 'xxx'.

This PR checks the exception and provides instructions on how to work with MFA tenants:

Tenant da086fa3-023f-4500-bf56-0f19d3065440 requires Multi-Factor Authentication (MFA). To access this tenant, use 'az login --tenant' to explicitly login to this tenant.

For the test, since CI still uses nosetests while we locally use pytest, it is difficult to verify captured logs in both test frameworks: https://docs.pytest.org/en/latest/logging.html#caplog-fixture

We can manually run the test with -o log_cli=True to check that the warning is displayed correctly:

pytest -o log_cli=True src/azure-cli-core/azure/cli/core/tests/test_profile.py::TestProfile::test_find_using_common_tenant_mfa_warning

[yonzhan]

add to S167

[qianwens]