installd: implement installApkVerity

This API read from an ashmem-backed fd and append the content to the end
of the given apk, then issue an ioctl to enable fsverity.

Note that the ioctl constants are not yet in upstream (thus the feature
is behind a flag), so we can't have them in the common header in
bionic/libc/kernel.  As the result, the constants are snapshot into the
file at this point.

Test: observed that ioctl is called (still waiting for kernel to ready)
Bug: 30972906

Change-Id: Ie05881e1e03d1b9a4d7faafa501420f0e22948ef