Remove ucloud_common and put its files under ucloud.common subpackage.

Remove individual config.py used by every component and put them into single config.py ucloud/config.py
Use /etc/ucloud/ucloud.conf for Environment Variables
Refactoring and a lot of it
Make ucloud repo a package and different components of ucloud a subpackage for avoiding code duplication.
Improved logging.

api/common_fields.py

@@ -1,7 +1,6 @@
 import os
 
-from config import etcd_client as client
-from config import VM_PREFIX
+from config import etcd_client, env_vars
 
 
 class Optional:
@@ -49,6 +48,6 @@ class VmUUIDField(Field):
         self.validation = self.vm_uuid_validation
 
     def vm_uuid_validation(self):
-        r = client.get(os.path.join(VM_PREFIX, self.uuid))
+        r = etcd_client.get(os.path.join(env_vars.get('VM_PREFIX'), self.uuid))
         if not r:
             self.add_error("VM with uuid {} does not exists".format(self.uuid))