If server is started without a JWT key, a message like the following is printed:
```
################################################################################
# ERROR:
# A value must be supplied for --auth_jwt_key. This value is used to create
# session tokens for users.
#
# Consider using the following randomly generated key:
# om3w95gMA2drT5xAdLd2Q5oE8fLw+Miz
################################################################################
```
Closes#1480.
Made log rotation for osquery results and status logs optional. This required writing the logwriter package which is a drop in replacement for lumberjack. We still use lumberjack if the log rotation flag --osquery_enable_log_rotation flag is set. Note that the performance of the default is quite a bit better than lumberjack.
BenchmarkLogger-8 2000000 747 ns/op
BenchmarkLumberjack-8 1000000 1965 ns/op
PASS
BenchmarkLogger-8 2000000 731 ns/op
BenchmarkLumberjack-8 1000000 2040 ns/op
PASS
BenchmarkLogger-8 2000000 741 ns/op
BenchmarkLumberjack-8 1000000 1970 ns/op
PASS
BenchmarkLogger-8 2000000 737 ns/op
BenchmarkLumberjack-8 1000000 1930 ns/op
PASS
