Add ro.boot.fstab_suffix and modify mount_all to use it

Currently the ReadDefaultFstab function, which calls GetFstabPath,
makes some assumptions about what the fstab will be called and where
it is located. This is being used by vold to set up userdata encryption
and for gsid, and is even used in the default boot control HAL, so it
has become quite baked.

The original way for a board to specify things to mount was to use the
"mount_all /path/to/fstab" command in init.rc. However, due to the
above functionality, the path after mount_all is no longer very useful,
as it cannot differ from the inferred path, or userdata encryption and
other features will be broken.

On Cuttlefish, we have an interest in being able to test alternative
userdata configurations (ext4 vs f2fs, encryption on/off, etc.) and
currently the only way to achieve this is to either a) modify the
ro.hardware or ro.hardware.platform properties, which breaks a bunch
of things like default HAL filenames, or regenerate our odm.img or
vendor.img filesystems. We can't simply install another fstab and
point to it with "mount_all".

This change allows the fstab path to be omitted from "mount_all", and
adds another property which overrides the existing checks for
fstab.${ro.hardware} and fstab.${ro.hardware.platform}. Specifying
${ro.boot.fstab_suffix} will cause fstab.${ro.boot.fstab_suffix}
to be checked first.

Bug: 142424832
Test: booted cuttlefish with 'mount_all ${ro.hardware} --late'
Test: booted cuttlefish with 'mount_all --late'
Test: booted cuttlefish with 'mount_all --late' and fstab_suffix=f2fs
Test: partially booted cuttlefish with 'mount_all ${ro.hardware}'
Test: partially booted cuttlefish with 'mount_all'
Change-Id: I3e10f66aecfcd48bdb9ebf1d304b7aae745cbd3c
7 files changed