globalDeploymentID was being read while it was being set.
Fixes race:
```
WARNING: DATA RACE
Write at 0x0000079605a0 by main goroutine:
github.com/minio/minio/cmd.connectLoadInitFormats()
github.com/minio/minio/cmd/prepare-storage.go:269 +0x14f0
github.com/minio/minio/cmd.waitForFormatErasure()
github.com/minio/minio/cmd/prepare-storage.go:294 +0x21d
...
Previous read at 0x0000079605a0 by goroutine 105:
github.com/minio/minio/cmd.newContext()
github.com/minio/minio/cmd/utils.go:817 +0x31e
github.com/minio/minio/cmd.adminMiddleware.func1()
github.com/minio/minio/cmd/admin-router.go:110 +0x96
net/http.HandlerFunc.ServeHTTP()
net/http/server.go:2136 +0x47
github.com/minio/minio/cmd.setBucketForwardingMiddleware.func1()
github.com/minio/minio/cmd/generic-handlers.go:460 +0xb1a
net/http.HandlerFunc.ServeHTTP()
net/http/server.go:2136 +0x47
...
```
* Reduce allocations
* Add stringsHasPrefixFold which can compare string prefixes, while ignoring case and not allocating.
* Reuse all msgp.Readers
* Reuse metadata buffers when not reading data.
* Make type safe. Make buffer 4K instead of 8.
* Unslice
With the current asynchronous behaviour in sending notification events
to the targets, we can't provide guaranteed delivery as the systems
might go for restarts.
For such event-driven use-cases, we can provide an option to enable
synchronous events where the APIs wait until the event is successfully
sent or persisted.
This commit adds 'MINIO_API_SYNC_EVENTS' env which when set to 'on'
will enable sending/persisting events to targets synchronously.
