Can you please include the whole log of this step, and maybe the script content too? Would make it way easier and faster to help you with the debugging 
I’d also suggest you to check these guides, to help with local debugging on your Mac/Linux:
- How to experiment with Bitrise configs locally, on your Mac/Linux
- How to debug your build locally / "It works on my Mac/PC but not on bitrise.io"
This seems like you provided an invalid parameter/option to the keytool command. Might be that you provided an invalid path - from this it seems the path specified was /android.keystore which should probably be ./android.keystore, as if the path starts with a / that means the file system root, not the repo root or the current directory.