Creation of backup driver fails for EBS with region formatting issue

## Summary

Creating an EBS backup driver fails with region formatting issue

## Detailed Information

apache-libcloud version 3.4.1 python 3.6

>>> cls = libcloud.get_driver(libcloud.DriverType.BACKUP, libcloud.DriverType.BACKUP.EBS)
>>> backup_driver = cls(constants.CONFIG["aws_access_key"], constants.CONFIG["aws_secret_key"], region="ap-south-1")
Traceback (most recent call last):
File "", line 1, in
File "/home/ec2-user/.local/lib/python3.6/site-packages/libcloud/backup/drivers/ebs.py", line 59, in __init__
self.connection.host = HOST % (region)
TypeError: not all arguments converted during string formatting

Unlike other AWS drivers, EBS does not have specific driver type per region. I suspect this is causing the issue.

Start with libcloud/backup/drivers/ebs.py at the constructor line shown in the traceback, then reproduce creation of the EBS backup driver with region="ap-south-1". Compare the region handling there with the other AWS drivers mentioned in the issue. Done means the driver initializes successfully for that region without the formatting TypeError.

Written by the indexing model from the issue text.