New Features + Refactoring

1. User can now use image name instead of image uuid when creation vm.
   For Example, now user can create an alpine vm using the following
   command
   ```shell
   ucloud-cli vm create --vm-name myvm --cpu 2 --ram '2GB' \
       --os-ssd '10GB' --image images:alpine
   ```
2. Instead of directly running code, code is now placed under a function
   main and is called using the following code
   ```python
   if __name__ == "__main__":
       main()
   ```
3. Multiprocess (Process) is used instead of threading (Thread) to update
   heart beat of host.
4. IP Address of vm is included in vm's status which is retrieved by the
   following command
   ```shell
   ucloud-cli vm status --vm-name myvm
   ```

api/schemas.py

@@ -18,6 +18,8 @@ import json
 import os
 import bitmath
 
+import helper
+
 from ucloud_common.host import HostPool, HostStatus
 from ucloud_common.vm import VmPool, VMStatus
 
@@ -207,22 +209,24 @@ class CreateVMSchema(OTPSchema):
         # Fields
         self.specs = Field("specs", dict, data.get("specs", KeyError))
         self.vm_name = Field("vm_name", str, data.get("vm_name", KeyError))
-        self.image_uuid = Field("image_uuid", str, data.get("image_uuid", KeyError))
+        self.image = Field("image", str, data.get("image", KeyError))
 
         # Validation
-        self.image_uuid.validation = self.image_uuid_validation
+        self.image.validation = self.image_validation
         self.vm_name.validation = self.vm_name_validation
         self.specs.validation = self.specs_validation
 
-        fields = [self.vm_name, self.image_uuid, self.specs]
+        fields = [self.vm_name, self.image, self.specs]
 
         super().__init__(data=data, fields=fields)
 
-    def image_uuid_validation(self):
-        images = client.get_prefix(IMAGE_PREFIX)
-
-        if self.image_uuid.value not in [i.key.split("/")[-1] for i in images]:
-            self.add_error("Image UUID not valid")
+    def image_validation(self):
+        try:
+            image_uuid = helper.resolve_image_name(self.image.value, client)
+        except Exception as e:
+            self.add_error(str(e))
+        else:
+            self.image_uuid = image_uuid
 
     def vm_name_validation(self):
         if resolve_vm_name(name=self.vm_name.value, owner=self.name.value):