Loosen tolerances on some tests on i386

Loosen tolerances on some tests on i386

and xfail a test that fails for not producing ConvergenceWarning.

Failure logs:
test_smoothing
https://buildd.debian.org/status/fetch.php?pkg=statsmodels&arch=i386&ver=0.9.0-3&stamp=1567157609&raw=0
test_multivariate_switch_univariate
https://buildd.debian.org/status/fetch.php?pkg=statsmodels&arch=i386&ver=0.12.0-1&stamp=1599693472&raw=0
TestMixedLM.test_compare_numdiff
salsa-ci for 0.14.2-1

As it only fails on i386 and isn't far wrong,
I suspect different rounding due to x87 excess precision

Author: Rebecca N. Palmer <rebecca_palmer@zoho.com>
Bug-Debian: partly https://bugs.debian.org/938949
Forwarded: no

Gbp-Pq: Name i386_loosen_test_tolerances.patch