A self link should only require one allocation, and we should skip
url.PathEscape() except when the path actually needs it.
Add a fuzz test to build random strings and verify them against
the optimized implementation. Add a new BenchmarkWatchHTTP_UTF8 that
covers when we have unicode names in the self link.
```
> before
BenchmarkGet-12 10000 118863 ns/op 17482 B/op 130 allocs/op
BenchmarkWatchHTTP-12 30000 38346 ns/op 1893 B/op 29 allocs/op
> after
BenchmarkGet-12 10000 116218 ns/op 17456 B/op 130 allocs/op
BenchmarkWatchHTTP-12 50000 35988 ns/op 1571 B/op 26 allocs/op
BenchmarkWatchHTTP_UTF8-12 50000 41467 ns/op 1928 B/op 28 allocs/op
```
Saves 3 allocations in the fast path and 1 in the slow path (the
slow path has to build the buffer and then call url.EscapedPath
which always allocates).
Kubernetes-commit: 389a8436b52db4936b56e08f07984da362c91f6b
Wojciech Tyczyński
j2gg0s
Clayton Coleman
Jordan Liggitt
Cao Shufeng
deads2k