otautil/roots.h includes <fstab/fstab.h>, but users of otautil/roots.h
don't need to explicitly depend on libfstab unless they have a real
need.
Also remove the unneeded include of <fstab/fstab.h> from
fsck_unshare_blocks.cpp.
Test: mmma -j bootable/recovery
Change-Id: Id3dc995a4769e631ab242843ee439bd94b2bf0bc
Build libinstall as a shared library. Also drop the dependency on the
global variables in common.h.
Test: unit tests pass, sideload an OTA
Change-Id: I30a20047768ce00689fc0e7851c1c5d712a365a0