Certain environments use WARN for serious logging; however, it's very
possible to have machines without some of the fingerprinted keys
(public-ipv4 and public-hostname specifcally). Setting log level to
INFO seems more consistent with this possibility.
* Allow server TLS configuration to be reloaded via SIGHUP
* dynamic tls reloading for nomad agents
* code cleanup and refactoring
* ensure keyloader is initialized, add comments
* allow downgrading from TLS
* initalize keyloader if necessary
* integration test for tls reload
* fix up test to assert success on reloaded TLS configuration
* failure in loading a new TLS config should remain at current
Reload only the config if agent is already using TLS
* reload agent configuration before specific server/client
lock keyloader before loading/caching a new certificate
* introduce a get-or-set method for keyloader
* fixups from code review
* fix up linting errors
* fixups from code review
* add lock for config updates; improve copy of tls config
* GetCertificate only reloads certificates dynamically for the server
* config updates/copies should be on agent
* improve http integration test
* simplify agent reloading storing a local copy of config
* reuse the same keyloader when reloading
* Test that server and client get reloaded but keep keyloader
* Keyloader exposes GetClientCertificate as well for outgoing connections
* Fix spelling
* correct changelog style
WARNing when someone has over 50 non-terminal allocs was just too
confusing.
Tested manually with `gc_max_allocs = 10` and bumping a job from `count
= 19` to `count = 21`:
```
2017/11/02 17:54:21.076132 [INFO] client.gc: garbage collection due to number of allocations (19) is over the limit (10) skipped because no terminal allocations
...
2017/11/02 17:54:48.634529 [WARN] client.gc: garbage collection due to number of allocations (21) is over the limit (10) skipped because no terminal allocations
```
The Client.allocs map now contains all AllocRunners again, not just
un-GC'd AllocRunners. Client.allocs is only pruned when the server GCs
allocs.
Also stops logging "marked for GC" twice.
Fixes https://github.com/hashicorp/nomad/issues/3454
Reliably reproduced the data race before by having a fingerprinter
change the nodes attributes every millisecond and syncing at the same
rate. With fix, did not ever panic.
