Replace pytest-sugar by pytest-instafail.

While pytest-sugar was nice to look at, it produced a lot of issues:

- Unusable on CI
- Unusable on OS X and Windows
- Garbage when terminal was resized during tests
- Missing space after test name since some while

This replaces it by pytest-instafail, which replaces the most important feature
of sugar, and on top of that, also works on CI.

.appveyor.yml

@@ -14,4 +14,4 @@ install:
   - C:\Python27\python -u scripts\dev\ci_install.py
 
 test_script:
-  - C:\Python34\Scripts\tox -e %TESTENV% -- -p "no:sugar" -v --junitxml=junit.xml
+  - C:\Python34\Scripts\tox -e %TESTENV% -- -v --junitxml=junit.xml

.travis.yml

@@ -37,7 +37,7 @@ install:
   - python scripts/dev/ci_install.py
 
 script:
-  - tox -e $TESTENV -- -p no:sugar -v --cov-report term tests
+  - tox -e $TESTENV -- -v --cov-report term tests
 
 after_success:
   - '[[ ($TESTENV == py34 || $TESTENV == py35) && $TRAVIS_OX == linux ]] && codecov -e TESTENV -X gcov'

tox.ini

@@ -34,7 +34,7 @@ deps =
     pytest-html==1.7
     pytest-mock==0.9.0
     pytest-qt==1.11.0
-    pytest-sugar==0.5.1
+    pytest-instafail==0.3.0
     pytest-travis-fold==1.2.0
     pytest-repeat==0.2
     six==1.10.0
@@ -46,7 +46,7 @@ deps =
     cherrypy==4.0.0
 commands =
     {envpython} scripts/link_pyqt.py --tox {envdir}
-    {envpython} -m py.test --strict -rfEsw --faulthandler-timeout=70 --cov --cov-report xml --cov-report=html --cov-report= {posargs:tests}
+    {envpython} -m py.test --strict -rfEsw --faulthandler-timeout=70 --instafail --cov --cov-report xml --cov-report=html --cov-report= {posargs:tests}
     {envpython} scripts/dev/check_coverage.py {posargs}
 
 [testenv:mkvenv]