xapian-bridge C port

endlessm/eos-sdk#2463
I think we need to be able to specify a different port to listen on. If I run the tests on a system where Xapian Bridge is already running (`xapian-bridge & make check`), they pass, but in the test logs I see this:
```
/daemon/starts-successfully: OK
/daemon/get-empty-fails: 
** (process:4822): ERROR **: Can't start Xapian bridge server: Could not listen on address 127.0.0.1, port 3004
OK
/daemon/get-returns-ok: OK
/daemon/get-query-returns-json: 
** (process:4829): ERROR **: Can't start Xapian bridge server: Could not listen on address 127.0.0.1, port 3004
OK
/daemon/put-creates-db: 
** (process:4830): ERROR **: Can't start Xapian bridge server: Could not listen on address 127.0.0.1, port 3004
OK
/daemon/put-lang-creates-db: 
** (process:4831): ERROR **: Can't start Xapian bridge server: Could not listen on address 127.0.0.1, port 3004
OK
/daemon/put-no-path-fails: OK
/daemon/put-meta-not-allowed: OK
/daemon/delete-removes-db: 
** (process:4834): ERROR **: Can't start Xapian bridge server: Could not listen on address 127.0.0.1, port 3004
OK
/daemon/delete-invalid-fails: OK
/daemon/delete-meta-not-allowed: OK
```
I assume it can't start because something is already listening on port 3004. That indicates to me that we should fail the test if the subprocess exited with an error, because now the tests are operating on the already-running daemon instead of the freshly-built one. (Strangely, I only see five failures to start the daemon, but there are eleven tests.)