Update OTA installer to understand SELinux filesystem labels

Modify the OTA installer to understand SELinux filesystem labels.

We do this by introducing new set_perm2 / set_perm2_recursive
calls, which understand SELinux filesystem labels. These filesystem
labels are applied at the same time that we apply the
UID / GID / permission changes.

For compatibility, we preserve the behavior of the existing
set_perm / set_perm_recursive calls.

If the destination kernel doesn't support security labels, don't
fail. SELinux isn't enabled on all kernels.

Bug: 8985290
Change-Id: I99800499f01784199e4918a82e3e2db1089cf25b