update holland.spec for new plugin directory structure

Combined similar plugins into fewer packages:
holland-common - Common support files for other plugins
holland-lvm - LVM support and generic plugins
holland-mysql - mysql based plugins (mysqldump,xtrabackup,etc)
holland-mysql-lvm - pseudo package to pull in holland-lvm+holland-mysql
                    to provide support for LVM snapshot based backups
                    for MySQL
holland-pgsql - postgres based plugins (pgdump)