Respect that status property when parsing fstab from device tree

For an fstab entry in device tree, fs_mgr now honors the status property
as done by linux. i.e. the node (in this case, the fstab entry) is
enabled if status is not set, "ok" or "okay". For every other value, the
node is considered as disabled.

Bug: 62127741
Test: Test sailfish w/ no status property, result: boots
Test: Test with status = "disabled", result: skips mounting /vendor
Test: Test with status = "ok", result: boots

Change-Id: I5ff8f710de2c54afc76b4af28108ca9075357ad1
Signed-off-by: Sandeep Patil <sspatil@google.com>