dockcross: Ignore deletion error when running in unprivileged LXC container
dockcross: Ignore deletion error when running in unprivileged LXC container

This commit workarounds the problem described in [1] and [2] by ignoring error
happening when deleting container in unprivileged LXC container.

Fixes #50

[1] https://circleci.com/docs/docker-btrfs-error/
[2] https://discuss.circleci.com/t/docker-error-removing-intermediate-container/70

dockcross/dockcross,dockcross/dockcross,dockcross/dockcross,thewtex/cross-compilers,thewtex/cross-compilers,dockcross/dockcross,thewtex/cross-compilers,thewtex/cross-compilers