Require INSTALL_PACKAGES permission

Although it's not technically necessary for the ephemeral installer
to hold the INSTALL_PACKAGES permission, it leads to a pretty
poor experience -- the user has to confirm ephemeral installation --
which is a primary reason for ephemeral apps.

Change-Id: Ic3f947d677964521cd4742f66c1c3fe808c4c55a
Fixes: 33073519
Test: manual; installed packages w/ and w/o INSTALL_PACKAGES and only the apps with INSTALL_PACKAGES were made the installer