Allow url as source of file to be deployed to host

This change allows the HostSystem and Genesis document to specify direct
URLs to files (for example, kubelet and kubectl) that are to be written
to the deployed hosts.

Change-Id: I1828d4a9e654537448631434b26b5becc4d2d717

doc/source/configuration/host-system.rst

@@ -138,7 +138,8 @@ Sample Document to run containers in Containerd runtime
 Files
 -----
 
-A list of files to be written to the host.  Files can be given as precise content or extracted from a tarball specified by url:
+A list of files to be written to the host.  Files can be given as precise
+content, extracted from a tarball specified by url, or downloaded from a url:
 
 .. code-block:: yaml
 
@@ -148,8 +149,10 @@ A list of files to be written to the host.  Files can be given as precise conten
         exact
         text
     - path: /etc/from-tar
-      tar_url: http://example.com/file
+      tar_url: http://example.com/file.tgz
       tar_source: dir/file.txt
+    - path: /etc/from-url
+      url: http://example.com/file
 
 Images
 ------

promenade/builder.py

@@ -54,6 +54,8 @@ class Builder:
             elif 'symlink' in file_spec:
                 data = file_spec['symlink']
                 islink = True
+            elif 'url' in file_spec:
+                data = _fetch_tar_url(file_spec['url'])
             elif 'tar_url' in file_spec:
                 data = _fetch_tar_content(file_spec['tar_url'],
                                           file_spec['tar_path'])

promenade/schemas/Genesis.yaml

@@ -23,6 +23,8 @@ data:
         mode:
           type: integer
           minimum: 0
+        url:
+          $ref: '#/definitions/url'
         tar_url:
           $ref: '#/definitions/url'
         tar_path:
@@ -35,6 +37,9 @@ data:
         - type: object
           required:
             - content
+        - type: object
+          required:
+            - url
         - type: object
           allOf:
             - type: object

promenade/schemas/HostSystem.yaml

@@ -37,6 +37,8 @@ data:
         mode:
           type: integer
           minimum: 0
+        url:
+          $ref: '#/definitions/url'
         tar_url:
           $ref: '#/definitions/url'
         tar_path:
@@ -57,6 +59,9 @@ data:
         - type: object
           required:
             - symlink
+        - type: object
+          required:
+            - url
         - type: object
           allOf:
             - type: object