add SysV-style init script for Linux

Signed-off-by: Thiago Rondon <thiago.rondon@gmail.com>
daemon mode save pid in /var/run/bdatum-backup.pid

Signed-off-by: Thiago Rondon <thiago.rondon@gmail.com>
typo

Signed-off-by: Thiago Rondon <thiago.rondon@gmail.com>
add support for status

Signed-off-by: Thiago Rondon <thiago.rondon@gmail.com>