Use canonical form of Docker folder when building TAR files

In `BuildImageCmdImpl#buildDockerFolderTar` a canonical form of the source files referenced in the Dockerfile is used. But the Docker folder is passed in the given form to the `CompressArchiveUtil`.

`CompressArchiveUtil#relativize` creates absolute TAR archive entries if the canonical form of the source files differs from the given form of the Docker folder. As a result, the Docker deamon can not find the files during the build. This can happen in case-insensitive file systems such as Windows, for example.

As a solution, the canonical form of the Docker folder must be used.