Add "--force-cross-build" argument to kolla-build

[Vikram Hosakote]

By default, "kolla-build" builds all containers using CentOS as the base image.

Due to this issue, kolla-build fails to build many containers on Ubuntu due to the following errors.

INFO:kolla.cmd.build:keystone:Error unpacking rpm package httpd-2.4.6-40.el7.centos.x86_64

INFO:kolla.cmd.build:keystone:error: unpacking of archive failed on file /usr/sbin/suexec: cpio: cap_set_file

INFO:kolla.cmd.build:keystone:error: httpd-2.4.6-40.el7.centos.x86_64: install failed

Hence, a new argument "--force-cross-build" must be added for kolla-build. When the user builds CentOS images on Ubuntu and vice-versa, the "--force-cross-build" argument must be explicitly specified. If not, kolla-build must throw as error like "Your host OS is Ubuntu and you are building CentOS containers. Please use the "--force-cross-build" flag to do this" so that the user knows what he/she is doing.

[Vikram Hosakote (vhosakot)]

Fixing this bug.

[Jeffrey Zhang (jeffrey4l)]

IIRC, on ubuntu, it is using aufs as stoage driver. the aufs is the root cause[0]. If you change the storage driver to others( btrfs, overlay etc), you should be able to cross build image.

So, no need add such a parameter. Add some note to the doc is enough.

[0] https://github.com/docker/docker/issues/6980

[Jeffrey Zhang (jeffrey4l)]

I can build different distro images by using the same OS.

like: build ubuntu, centos images on archlinux node. So this should not be a issue.

i will mark this invalid.