* Modified tests to use tlogger.
* Fail on errors, with error expectations.
* Added expects and MixedCapsed grpclb_config tests
* Moved tlogger to grpctest, moved leakcheck tester to grpctest.go
* Added ExpectErrorN()
* Removed redundant leak checks
* Fixed new test
* Made tlogger globals into tlogger methods
* ErrorsLeft -> EndTest
* Removed some redundant lines
* Fixed error in test and empty map in EndTest
Also includes:
- Export `NewLoggerFromConfigString` so it can be also used when config string is specified in another way (e.g. command line flag)
- Export `Logger` so user can install custom sink
- Add temp file sink implementation
