title: Can't Signing and pushing trust metadata in Notary
body: <p>I am implementing Notary in a virtual machine. To have a reference, I have a docker registry on <strong>host A</strong> and I want to deploy Notary Server, Signer and CLI on <strong>host B</strong> to get push images to registry and sign them from different machine. However, the problem happens when I try to sign an image on host B of Notary with role targets. The following error message appears:</p>
  
  <pre><code>[root@HostB ~]# docker push my.registry:443/galera-leader-proxy:v1.0.0
  The push refers to a repository [my.registry:443/galera-leader-proxy]
  5f70bf18a086: Layer already exists
  1de59669c563: Layer already exists
  17dd9fb03617: Layer already exists
  26093688fdcb: Layer already exists
  e08be57f5919: Layer already exists
  v1.0.0: digest: sha256:6e48967416ea76ba2825511da7b05107a41f585629009d18ccbf30a1e1ce0e5a size: 2179
  Signing and pushing trust metadata
  ERRO[0000] couldn't add target to targets: could not find necessary signing keys, at least one of these keys must be available: b92334936cf0a0f0e3fb9dce459212537387847ee288ce27762fd54850f89e6f
  Failed to sign "my.registry:443/galera-leader-proxy":v1.0.0 - could not find necessary signing keys, at least one of these keys must be available: b92334936cf0a0f0e3fb9dce459212537387847ee288ce27762fd54850f89e6f
  Error: could not find signing keys for remote repository my.registry:443/galera-leader-proxy, or could not decrypt signing key: could not find necessary signing keys, at least one of these keys must be available: b92334936cf0a0f0e3fb9dce459212537387847ee288ce27762fd54850f89e6f
  </code></pre>
  
  <p>Docker image is pushed to the registry but at the time of signing I get the error message that does not find the "<em>keys</em>" to sign. However, if I see the keys of notary, the key that can not be found to sign if it is available. Then I do not know why this happens or that I have configured badly:</p>
  
  <pre><code>[root@HostB ~]# dockernotary key list
  
  ROLE        GUN                          KEY ID                                                              LOCATION
  ----        ---                          ------                                                              --------
  root                                     7b8139837e3bf8b013f69bf0750d46ba0f70a6a6d9640eadcb592ae8a5ae2c0d    /home/gmaurelia/.docker/trust/private
  snapshot    ...43/galera-leader-proxy    92cf3f72d573cab7b6045f72fe224a4ccf786e9ddd29c89b3a542b610061c763    /home/gmaurelia/.docker/trust/private
  targets     ...43/galera-leader-proxy    b92334936cf0a0f0e3fb9dce459212537387847ee288ce27762fd54850f89e6f    /home/gmaurelia/.docker/trust/private
  
  
  PD: alias dockernotary="notary -c 
  /home/gmaurelia/.docker/trust/config.json -d 
  /home/gmaurelia/.docker/trust/ -s https://notary-server:4443"
  </code></pre>
  
  <p>I can not even sign under the role: targets or targets/releases</p>