Increase TEMPEST_THREADS to 4

Change-Id: If0bf0443b7c32eb16edcf5819210e0398fad5519
diff --git a/tcp_tests/settings.py b/tcp_tests/settings.py
index 83968e2..54aafae 100644
--- a/tcp_tests/settings.py
+++ b/tcp_tests/settings.py
@@ -82,7 +82,7 @@
 TEMPEST_IMAGE_VERSION = os.environ.get('TEMPEST_IMAGE_VERSION', 'pike')
 TEMPEST_PATTERN = os.environ.get('TEMPEST_PATTERN', 'tempest')
 TEMPEST_TIMEOUT = int(os.environ.get('TEMPEST_TIMEOUT', 60 * 60 * 10))
-TEMPEST_THREADS = int(os.environ.get('TEMPEST_THREADS', 2))
+TEMPEST_THREADS = int(os.environ.get('TEMPEST_THREADS', 4))
 TEMPEST_EXTRA_ARGS = os.environ.get('TEMPEST_EXTRA_ARGS', '')
 TEMPEST_TARGET = os.environ.get('TEMPEST_TARGET', 'gtw01')
 SALT_VERSION = os.environ.get('SALT_VERSION', '2017.7')