bug: addPortToVS reference to formatVSPort

formatVSPort is an interface function and is not available from an
ophandler. addPortToVS can live w/o formatVSPort, just show the plain
text port number.
pass exception code to RacktablesError constructor

changed funcs: registerOpHandler, registerTabHandler
make RackTablesError::INTERNAL the default code

There are places where a RackTablesError object is created using only
one constructor parameter - the error message. This leads to unhandled
exception while dispatching such an exception.

This change forces RackTablesError::INTERNAL as a default value
don't use getAttrMap where possible

getAttrMap is a heavy function. It uses temporary tables and scans many
rows, but in many cases the result of this work is thrown away. The
query this function makes is in top of my sql slow queries log.
I've made two lightweight DB functions: getAttrType, getObjTypeAttrMap
and used them where possible.

getStickerSearchResults: use getAttrType
searchByMgmtHostname: idem
scanAttrRelativeDays: idem
supplementAttrMap: idem