init: harden socket creation against symlinks

Instead of using chown, use the symlink safe lchown.

Instead of using chmod, use the symlink safe fchmodat
with AT_SYMLINK_NOFOLLOW.

Fix a bug where the SELinux filesystem creation context may
not be restored, and some memory not freed, if bind() fails.

Check the return values from the chown/chmod calls and unlink
the files if it ever fails.

Bug: 27337831
Change-Id: I3343786f5a4eefda7bbb8317f2eca16bd21003c0