Fix invalid path character on windows

Replaces ':' as path character in tor_dirmgr::src::storage::sqlite::SqliteStore::save_blob_internal which is a reserved character on NTFS / windows. The patch fixes the following unit tests on windows:

• tor_dirmgr::src::storage::sqlite::test::consensus
• tor_dirmgr::src::lib::test::load_and_store_internals
• tor_dirmgr::src::lib::test::make_consensus_request
• tor_dirmgr::src::lib::test::expand_response

I temporarily #[cgf(...)] out the unit tests in tor_config that require a bug fix in shellexpand to pass (s. !274 (merged) ).