Summary: Make `library.sh` read `$HGTEST_GETDB_PATH` for `getdb.sh` location. Unify `getdb.sh` used by infinitepush and hgsql into one. Reviewed By: ryanmce Differential Revision: D6974635 fbshipit-source-id: 55bcebfbdaca7f43fb0cfca0d3e089e76cf9f24e