Test failures on Ubuntu with PySide2

@nicolasap-dm reports test failures on ubuntu with pyside2.

In order to setup the environment and run the testsuite, run the following commands -
```
python etstool.py install --toolkit=pyside2 --editable
python etstool.py test --toolkit=pyside2
```

This is the first failure that is observed -

```
ERROR: test_save_as (pyface.tests.test_file_dialog.TestFileDialog)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/ndemitri/repos/enthought/pyface/pyface/tests/test_file_dialog.py", line 100, in test_save_as
self.dialog.close()
File "/home/ndemitri/repos/enthought/pyface/pyface/ui/qt4/file_dialog.py", line 103, in close
self.control.selectedNameFilter()
ValueError: '' is not in list
```

output of edm list for environment

```
$ edm list
# Packages in environment 'pyface-test-3.6-pyside2'
# prefix: '/home/ndemitri/.edm/envs/pyface-test-3.6-pyside2'
appdirs 1.4.3-1 enthought/free
coverage 4.3.4-1 enthought/free
distribute_remove 1.0.0-4 enthought/free
flake8 3.8.4-4 enthought/free
flake8_ets 1.0.0-1 enthought/free
freeglut 2.8.1-2 enthought/free
freetype 2.10.0-7 enthought/free
harfbuzz 2.6.4-4 enthought/free
importlib_metadata 4.4.0-3 enthought/free
importlib_resources 3.3.0-1 enthought/free
libjpeg 7.0-5 enthought/free
liblcms2 2.11-1 enthought/free
libopenjpeg 2.4.0-2 enthought/free
libpng 1.6.37-1 enthought/free
libtiff 4.0.10-10 enthought/free
mccabe 0.6.1-1 enthought/free
mkl 2018.0.3-2 enthought/free
numpy 1.17.4-1 enthought/free
packaging 20.9-1 enthought/free
pillow 7.2.0-3 enthought/free
pip 20.0.2-4 enthought/free
pycodestyle 2.6.0-1 enthought/free
pyface 7.3.0-4 enthought/free
pyflakes 2.2.0-1 enthought/free
pygments 2.8.1-1 enthought/free
pyparsing 2.2.0-1 enthought/free
setuptools 41.6.0-5 enthought/free
six 1.15.0-1 enthought/free
traits 6.3.1-1 enthought/free
traitsui 7.2.1-2 enthought/free
typing 3.7.4.1-1 enthought/free
typing_extensions 3.7.4.1-1 enthought/free
zipp 3.4.0-2 enthought/free
```