init: only fsck hfs+ when booting from hfs+

Only fsck an HFS+ partition when we booted from an HFS+ partition. This
should only be true on AppleTV where we need to ensure the HFSX volume
is clean before mounting. It is false on other MacOS dual-boot
configurations where HFS+ partitions are present. This resolves #2929,
Merge pull request #2936 from chewitt/fsck_hfsplus_init

init: only fsck hfs+ when booting from hfs+