Send signals to tasks with dynamicsecrets in templates after agent restart

[tantra35]

This PR solve #4226

[nickethier]

Closing this since the allocrunner and taskrunner have changed pretty drastically with the 0.9 release. If you want to rebase against master again we'll gladly look at a new PR. Sorry this languished due to all the 0.9 client refactor work

[tantra35]

@nickethier just check this behavior in nomad 0.9.3 and it doesn't solve #4226, so after restart nomad agent allocation that uses dynamic secrets after re-render

2019-06-14T19:54:04.886+0300 [INFO ] client.consul: discovered following servers: servers=192.168.142.102:4647,192.168.142.101:4647,192.168.142.103:4647
2019-06-14T19:54:04.902+0300 [INFO ] client: node registration complete
2019/06/14 19:54:04.975911 [INFO] (runner) creating new runner (dry: false, once: false)
2019/06/14 19:54:04.976172 [INFO] (runner) creating watcher
2019/06/14 19:54:04.976323 [INFO] (runner) starting
2019/06/14 19:54:05.208804 [INFO] (runner) rendered "(dynamic)" => "/var/lib/nomad/alloc/b8aff9c0-b257-d633-1674-ec3020049ca6/vault_debug_task/secrets/consul_token.env"

doesn't restarted

[github-actions]

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