fix: ImportError when locustio is not installed

CHANGELOG.md

@@ -11,6 +11,7 @@
 **Bugfixes**
 
 - fix extend with testcase reference in format version 2
+- fix ImportError when locustio is not installed
 
 ## 2.2.0 (2019-06-24)
 

httprunner/cli.py

@@ -91,14 +91,12 @@ def main_hrun():
 def main_locust():
     """ Performance test with locust: parse command line options and run commands.
     """
-    # monkey patch ssl at beginning to avoid RecursionError when running locust.
-    from gevent import monkey; monkey.patch_ssl()
-
-    import multiprocessing
-    import sys
-    from httprunner import logger
-
     try:
+        # monkey patch ssl at beginning to avoid RecursionError when running locust.
+        from gevent import monkey; monkey.patch_ssl()
+        import multiprocessing
+        import sys
+        from httprunner import logger
         from httprunner import locusts
     except ImportError:
         msg = "Locust is not installed, install first and try again.\n"