erofs-utils: support selinux file contexts

Add --file-contexts flag that allows passing a selinux
file_context file to setup file selabels.

Reviewed-and-tested-by: Li Guifu <bluce.lee@aliyun.com>
Link: https://lore.kernel.org/r/20200608130854.16953-1-hsiangkao@aol.com
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
10 files changed