Minor cloudcafe updates for security groups tests

- Adding LinuxClient delete_file method
- Adding networks common constants
- Updating security groups data plane delay config default value

Change-Id: I0ee0c15a501270c3a7b7b6ab02be93917c4618a9

cloudcafe/compute/common/clients/remote_instance/linux/linux_client.py

@@ -252,6 +252,16 @@ class LinuxClient(RemoteInstanceClient):
         if output:
             return output.rstrip('\n') == 'File exists'
 
+    def delete_file(self, file_path):
+        """
+        Deletes the file.
+        @param file_path: Path to the file
+        @type file_path: string
+        """
+
+        command = 'rm {file_path}'.format(file_path=file_path)
+        self.ssh_client.execute_command(command)
+
     def generate_mountpoint(self, prefix=None):
         """
         Generates a string to use as a path for mounting drives on the