ci: use virtualenv to avoid race conditions

Desktop QA tests also use Pytest packages and their versions are
different, so we can't install them globally, it needs to be done per
build using `WORKSPACE_TMP` as destination.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

ci/Jenkinsfile

@@ -70,6 +70,10 @@ pipeline {
     PYTHONPATH = "${SQUISH_DIR}/lib:${SQUISH_DIR}/lib/python:${PYTHONPATH}"
     LD_LIBRARY_PATH = "${SQUISH_DIR}/lib:${SQUISH_DIR}/python3/lib:${LD_LIBRARY_PATH}"
 
+    /* Avoid race conditions with other builds using virtualenv. */
+    VIRTUAL_ENV = "${WORKSPACE_TMP}/venv"
+    PATH = "${VIRTUAL_ENV}/bin:${PATH}"
+
     TESTRAIL_URL = 'https://ethstatus.testrail.net'
     TESTRAIL_PROJECT_ID = 17
 
@@ -87,7 +91,8 @@ pipeline {
 
     stage('Deps') {
       steps { script {
-        sh 'pip3 install --user -r requirements.txt'
+        sh "python3 -m venv ${VIRTUAL_ENV}"
+        sh 'pip3 install -r requirements.txt'
       } }
     }