Fix/Update some tests and make some info messages more similar to original version of Dub

workaround dlang/dub-registry#341 by using more specific search term ...

- using a [phrase](https://docs.mongodb.com/manual/reference/operator/query/text/#phrases)
  search to limit the number of results

split dub search test ...

- to better localize errors

capture and log output of dub search failures

replace all usages of `exit` ...

- those skipped the ERR trap
- add die function to exit with line number and message

unify flags and error handling ...

- also add trap ERR handler to report exact error location

implement search command ...

- queries all package suppliers and outputs any found package