Paginate backup list api

* Order list by updated at to show latest first
* Add pagination support for backup list and instance backup
  list
* Add tests for pagination and ordering

Implements: blueprint paginate-backup-list

Change-Id: Ie98bd2bc0500dfe4bbe0bb8b420ad80ad7f5a5df
Removes privilege modification for MYSQL_BASE_DIR

Reasons:
- No usage of the path MYSQL_BASE_DIR in the method.
- 2 Files used in the method are both in different locations
  /tmp/my.cnf.tmp and /etc/mysql/my.cnf
- It is just a hanging line of code without any reasons.

Changes:
- privilege modification line removed from code.

Change-Id: I676f7faaf1e7b78c5d0f9f79b622f230ae2b9740
Closes-Bug: #1261854
Merge "Paginate backup list api"
Removes directory creation prior to _tmp_mount

Reasons:
- Directory creation is included in VolumeMountPoint.mount method.
- No need to repeat the steps before calling the mount method.

Changes:
- Removed directory creation prior to calling _tmp_mount.
- Test updated to reduce number of utils.execute,
  as we now have one less call in the code.

Change-Id: I5136f1ce537c919ff2e009cd617f33925d955e88
Closes-Bug: #1261905
make the bin scripts called with main()

This will make everything easier to manage and callable by other python
scripts/modules if you need to depend on the module. Others can then
just call the main() function instead of executing the script.

Closes-Bug: #1261823

Change-Id: I5e94ee19bd4f7a69d7ca5efc6288d402520cd5bf
Merge "Removes privilege modification for MYSQL_BASE_DIR"
Merge "Removes directory creation prior to _tmp_mount"
Merge "make the bin scripts called with main()"