dist: debian: install python modules to dist-packages, not site-packages
dist: debian: install python modules to dist-packages, not site-packages

Debian, in its wisdom, installs packages into the dist-packages
directory instead of the standard site-packages directory (well,
it does make sense to separate distribution provided packages from
administrator provided packages, but still). As a result, when running
cqlsh, python doesn't find cqlshlib in its path and fails.

Fix by overriding with --install-lib.

Fixes #112.

scylladb/scylla-tools-java,scylladb/scylla-tools-java,scylladb/scylla-tools-java,scylladb/scylla-tools-java