Add Honeycomb tracing to all Boulder components which act as
HTTP servers, gRPC servers, or gRPC clients. Add many values
which we currently emit to logs to the trace spans. Add a way to
configure the Honeycomb integration to our config files, and by
default configure all of our tests to "mute" (send nothing).
Followup changes will refine the configuration, attempt to reduce
the new dependency load, and introduce better sampling.
Part of https://github.com/letsencrypt/dev-misc-tickets/issues/218
Unit tests are confirmed to pass:
```
~/go/src/golang.org/x/net$ git log --pretty=format:'%h' -n 1
2180aed
~/go/src/golang.org/x/net$ go test ./...
ok golang.org/x/net/bpf 0.494s
ok golang.org/x/net/context 0.058s
ok golang.org/x/net/context/ctxhttp 0.104s
? golang.org/x/net/dict [no test files]
ok golang.org/x/net/dns/dnsmessage 0.074s
ok golang.org/x/net/html 0.097s
ok golang.org/x/net/html/atom 0.002s
ok golang.org/x/net/html/charset 0.020s
ok golang.org/x/net/http/httpguts 0.028s
ok golang.org/x/net/http/httpproxy 0.003s
ok golang.org/x/net/http2 125.352s
ok golang.org/x/net/http2/h2c 0.015s
? golang.org/x/net/http2/h2i [no test files]
ok golang.org/x/net/http2/hpack 0.042s
ok golang.org/x/net/icmp 0.002s
ok golang.org/x/net/idna 0.012s
? golang.org/x/net/internal/iana [no test files]
ok golang.org/x/net/internal/socket 4.560s
ok golang.org/x/net/internal/socks 0.222s
ok golang.org/x/net/internal/sockstest 0.015s
ok golang.org/x/net/internal/timeseries 0.020s
ok golang.org/x/net/ipv4 0.053s
ok golang.org/x/net/ipv6 0.043s
ok golang.org/x/net/nettest 1.057s
ok golang.org/x/net/netutil 0.819s
ok golang.org/x/net/proxy 0.039s
ok golang.org/x/net/publicsuffix 0.146s
ok golang.org/x/net/trace 0.007s
ok golang.org/x/net/webdav 0.091s
ok golang.org/x/net/webdav/internal/xml 0.010s
ok golang.org/x/net/websocket 0.026s
ok golang.org/x/net/xsrftoken 0.019s
```
Aaron Gable
Daniel McCarney