Bundle proc_bootconfig permission into read_fstab

fs_mgr::ReadDefaultFstab calls fs_mgr:ReadFstabFromDt() which eventually
calls fs_mgr_get_boot_config_from_bootconfig_source to read boot config.
Therefore bundle permission to read proc_bootconfig. This resolves some
selinux denials for update_engine

Test: th
Change-Id: Ia8bd94eb33a38ccd939577b54910645fec4ccda8
2 files changed