Allow shell command to accept std input stream.

Incremental and pm installs use stdin to provide APK data. This change
allows Jetpack to test incremental installs.

Bug: 162316399
Test: API change, already used in CTS
Test: atest PackageManagerShellCommandTest
Change-Id: I0a891535a7ff0b2a3459b03be56c6798e30086b6