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

.vsts/linux-buildbot.yml

@@ -54,6 +54,7 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'
 - script: python3 Tools/ssl/multissltests.py --steps=library --base-directory $(build.sourcesDirectory)/multissl --openssl $(OPENSSL) --system Linux
   displayName: 'python multissltests.py'
@@ -67,5 +68,5 @@ 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

@@ -53,6 +53,7 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'
 - script: python3 Tools/ssl/multissltests.py --steps=library --base-directory $(build.sourcesDirectory)/multissl --openssl $(OPENSSL) --system Linux
   displayName: 'python multissltests.py'
@@ -70,7 +71,7 @@ steps:
 - script: ./venv/bin/python -m test.pythoninfo
   displayName: 'Display build info'
 
-- script: ./venv/bin/python -m coverage run --pylib -m test --fail-env-changed -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 --fail-env-changed -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

@@ -31,6 +31,7 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'
 - script: python3 Tools/ssl/multissltests.py --steps=library --base-directory $(build.sourcesDirectory)/multissl --openssl $(OPENSSL) --system Linux
   displayName: 'python multissltests.py'

.vsts/linux-pr.yml

@@ -53,6 +53,7 @@ steps:
     liblzma-dev
     libffi-dev
     uuid-dev
+    xvfb
   displayName: 'Install dependencies'
 - script: python3 Tools/ssl/multissltests.py --steps=library --base-directory $(build.sourcesDirectory)/multissl --openssl $(OPENSSL) --system Linux
   displayName: 'python multissltests.py'
@@ -71,5 +72,5 @@ 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'