fix: fix unknown os vendor on alpine

[eraserix]

The error was:

1. Alpine does no longer provide VERSION_CODENAME in /etc/os-release
2. The code refused to return a valid OsInfo struct from parsing os-release and just set all the members to "unknown".
3. Vendor was no longer set, but it is required to install system packages, i.e. to know if apk or apt-get needs to be called
   Feature fails to install

The implemented fix makes OsInfo parsing return whatever information it can get. Undefined fields are set to "unknown".