use shell to open v4 signature file

BUG: 133435829
Test: atest PackageManagerShellCommandIncrementalTest
Change-Id: I8e57b00f042f8b6c85d5f905460dd2da6199accc
(cherry picked from commit cdbcb34c2babcd2523acbe3d359855fe1155e7c3)
2 files changed