refactor parameterization:

parameter value now can be in three types:
(1) data list
(2) call built-in parameterize function
(3) call custom function in debugtalk.py

tests/data/demo_parameters.yml

@@ -1,13 +1,13 @@
 - config:
     name: "user management testset."
     parameters:
-        - user_agent: Random
-        - app_version: Sequential
+        - user_agent: ["iOS/10.1", "iOS/10.2", "iOS/10.3"]
+        - app_version: ${gen_app_version()}
+        - username: ${parameterize(account.csv)}
     variables:
         - user_agent: 'iOS/10.3'
         - device_sn: ${gen_random_string(15)}
         - os_platform: 'ios'
-        - app_version: '2.8.6'
     request:
         base_url: $BASE_URL
         headers:
@@ -17,7 +17,7 @@
         - token
 
 - test:
-    name: get token with $user_agent and $app_version
+    name: get token with $user_agent and $app_version, username $username
     api: get_token($user_agent, $device_sn, $os_platform, $app_version)
     extract:
         - token: content.token