read_logs.py should have --file option

[manishtomar]

When testing using docker or devvm I tend to run otter manually (not via sv) and transfer all its logs to a file. Currently, I name that file current and use --directory option to point to the directory where this file is located. It becomes cumbersome to use the command for multiple files (they need to be in different directories). It will be nice if read_logs.py can take file as an argument using --file option.