Teach QTestLib to read QTEST_ENVIRONMENT to expand blacklist keywords

Can be used by CI system to set QTEST_ENVIRONMENT="ci", allowing test to
be blacklisted only for the CI.

Task-number: QTBUG-59564
Change-Id: I7088abb888c179bafc621f11191efbc45c37b179
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/testlib/qtestblacklist.cpp

@@ -82,7 +82,9 @@ QT_BEGIN_NAMESPACE
         msvc-2010
 
   Keys are lower-case.  Distribution name and version are supported if
-  QSysInfo's productType() and productVersion() return them.
+  QSysInfo's productType() and productVersion() return them. Keys can be
+  added via the space-separated QTEST_ENVIRONMENT environment variable.
+
   The other known keys are listed below:
 */
 
@@ -184,6 +186,11 @@ static QSet<QByteArray> activeConditions()
         }
     }
 
+    if (qEnvironmentVariableIsSet("QTEST_ENVIRONMENT")) {
+        for (const QByteArray &k : qgetenv("QTEST_ENVIRONMENT").split(' '))
+            result.insert(k);
+    }
+
     return result;
 }