init-container in rust

[prekucki]

• cleanup logging to log crate
• port seccomp: runtime/init-container/src/seccomp.c to rinit.
• rewrite rinit/src/initramfs.rs to rust stdlib. #193
• remove macros: check_bool!, etc. #194
• clean rinit/src/network.rs, less copying, OwnedFd instad of c_int for descriptors. #196