Support local volume in "registry"

[kojiha]

The changes fix following issue to enable local volume support in "registry"

• Fixed issue in registry storage path when persistent storage is not enabled.
  It also upgrades docker registry to 2.6.2.

[kojiha]

I have posted issue #1582 for this pull-request.

[kojiha]

Just to make sure that the changes are very simple, I put diff from previous revision.

diff -r repo/packages/R/registry/1/marathon.json.mustache repo/packages/R/registry/2/marathon.json.mustache
16,18c16,19
<     {{#storage.persistence.external.enable}}          
<     "STORAGE_PATH": "{{storage.storage_path}}",
<     {{/storage.persistence.external.enable}}  
---
>     {{^storage.persistence.enable}}
>     "REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY": "{{storage.storage_path}}",
>     {{/storage.persistence.enable}}
>     {{#storage.persistence.enable}}
21c22,23
<     {{/storage.persistence.external.enable}}  
---
>     {{/storage.persistence.external.enable}}
>     {{/storage.persistence.enable}} 
diff -r repo/packages/R/registry/1/package.json repo/packages/R/registry/2/package.json
5c5
<   "version": "2.5.1-0.2",
---
>   "version": "2.6.2-0.1",
diff -r repo/packages/R/registry/1/resource.json repo/packages/R/registry/2/resource.json
10c10
<         "registry-docker": "registry:2.5.1"
---
>         "registry-docker": "registry:2.6.2"