In docker image/other rootfs scans with SCIO we are always
scanning for system packages before we scan for application
packages, and we were not being able to use the distro
information as this was being detected in application
package scans happening later. So in this commit we are
also adding os-release file parser to system package handler.

Signed-off-by: Ayan Sinha Mahapatra <ayansmahapatra@gmail.com>

Update debian, rpm and alpine package assembly to get
distro identifier and then set this properly to
created package, dependency and package_uid instances.

Reference: #3443
Signed-off-by: Ayan Sinha Mahapatra <ayansmahapatra@gmail.com>

Reference: #3726
Reference: package-url/purl-spec#171
Reference: package-url/purl-spec#159
Signed-off-by: Ayan Sinha Mahapatra <ayansmahapatra@gmail.com>

Signed-off-by: Ayan Sinha Mahapatra <ayansmahapatra@gmail.com>