Handle edge case when allocation create/modify time difference is les…

* 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

Task route hierarchy in the UI

Now that there is a task detail page, some of the content from
the allocation detail page is better suited there.

Drilling into a task from an allocation transitions to the task
heirarchy.

Vendor update to consul template 0.19.4

Clean vendored packages

Makefile typos

Fixed test and moved constants into standalone func

Better docs for docker.endpoint option

Clarify Name config

I'm not going to leave a review comment just to uppercase one dumb letter

Fixes https://github.com/hashicorp/nomad/issues/3517

Add support for passing device into docker driver

Fixes https://github.com/hashicorp/nomad/issues/3533

Fixes bug with display message logic due to deprecating GenericSource…

Fixes bug with display message logic due to deprecating GenericSource. Also added more test cases to cover a bunch more edge cases

In #3520, work was done to true up the defaults for Nomad resource
stanzas with the documentation.  This fixes the tests that I
accidentally broke in the process.  Some questions were raised about
using dynamic elements as part of expects, which is why I opted to
copy the MinResources pattern.   During this refactor I also noticed
that structs.go had a similar issue and an inconsistent minium for CPU.

Updated Troubleshooting section of Vault Integration docs

Updated Troubleshooting section of Vault Integration docs to mention the policy requirements for certain version combinations of Vault and Nomad, due to changes in Vault default policy and Nomad's vendored Vault lease renewal API.