rename testset => testcase

tests/data/demo_parameters.yml

@@ -1,5 +1,5 @@
 - config:
-    name: "user management testset."
+    name: "user management testcase."
     parameters:
         - user_agent: ["iOS/10.1", "iOS/10.2", "iOS/10.3"]
         - username-password:

tests/data/demo_testcase_functions.yml

@@ -1,5 +1,5 @@
 - config:
-    name: "create user testsets."
+    name: "create user testcases."
     variables:
         - user_agent: 'iOS/10.3'
         - device_sn: ${gen_random_string(15)}

tests/data/demo_testcase_layer.yml

@@ -1,5 +1,5 @@
 - config:
-    name: "user management testset."
+    name: "user management testcase."
     variables:
         - user_agent: 'iOS/10.3'
         - device_sn: ${gen_random_string(15)}

tests/data/demo_testcase_variables.yml

@@ -1,5 +1,5 @@
 - config:
-    name: "create user testsets."
+    name: "create user testcases."
     variables:
         - device_sn: 'HZfFBh6tU59EdXJ'
     request: