[3.6] Enable GUI tests in VSTS Linux builds via xvfb-run (GH-7890)

(cherry picked from commit 3f197f94d6)

.vsts/linux-buildbot.yml

@@ -49,6 +49,7 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'
 
 - script: ./configure --with-pydebug
@@ -60,5 +61,5 @@ steps:
 - script: make pythoninfo
   displayName: 'Display build info'
 
-- script: make buildbottest TESTOPTS="-j4 -uall,-cpu"
+- script: xvfb-run make buildbottest TESTOPTS="-j4 -uall,-cpu"
   displayName: 'Tests'

.vsts/linux-coverage.yml

@@ -48,6 +48,7 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'
 
 
@@ -63,7 +64,7 @@ steps:
 - script: ./venv/bin/python -m test.pythoninfo
   displayName: 'Display build info'
 
-- script: ./venv/bin/python -m coverage run --pylib -m test -uall,-cpu -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_multiprocessing_spawn -x test_concurrent_futures
+- script: xvfb-run./venv/bin/python -m coverage run --pylib -m test -uall,-cpu -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_multiprocessing_spawn -x test_concurrent_futures
   displayName: 'Tests with coverage'
 
 - script: source ./venv/bin/activate && bash <(curl -s https://codecov.io/bash)

.vsts/linux-deps.yml

@@ -27,4 +27,5 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'

.vsts/linux-pr.yml

@@ -48,6 +48,7 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'
 
 
@@ -64,5 +65,5 @@ steps:
 - script: ./python Tools/scripts/patchcheck.py --travis true
   displayName: 'Run patchcheck.py'
 
-- script: make buildbottest TESTOPTS="-j4 -uall,-cpu"
+- script: xvfb-run make buildbottest TESTOPTS="-j4 -uall,-cpu"
   displayName: 'Tests'