DEVOPS-4623: Unit tests failures: Exception: Warning: proc_open(): fork failed - Cannot allocate memory

- split app code into separate unit testsuite

Author: abeeskau

dev/tests/unit/phpunit.xml.dist

@@ -12,7 +12,10 @@
          beStrictAboutTestsThatDoNotTestAnything="false"
          bootstrap="./framework/bootstrap.php"
         >
-    <testsuite name="Magento Unit Tests">
+    <testsuite name="Magento_Unit_Tests_App_Code">
+        <directory suffix="Test.php">../../../app/code/*/*/Test/Unit</directory>
+    </testsuite>
+    <testsuite name="Magento_Unit_Tests_Other">
         <directory suffix="Test.php">../../../app/code/*/*/Test/Unit</directory>
         <directory suffix="Test.php">../../../lib/internal/*/*/Test/Unit</directory>
         <directory suffix="Test.php">../../../lib/internal/*/*/*/Test/Unit</directory>