build: Update install tools packaging for target-files support

Modifies "build: ota: Support for install tools in /tmp/install" to
support signing steps being split from build steps.

Package install files into target-files INSTALL path
Read from target-files for OTA package creation

Change-Id: I64f919c2a757b5474f6cc5f82bd6c33c2a8b558a
2 files changed