Merge pull request #12 from eagafonov/master

[PKG][OPENSSH] Create /var/empty whenever sshd is start
Add host configuration for opkg

Host's OPkg is going to be used to install packages into rootfs image
rather than dirty 'make install'
Implement $(pkg)-install-target with 'opkg-cl install'

$(pkg)-install-target enforces opkg package creation
and installs the package into rootfs output directory
Force files overwrite while installing packages into target