Added pillar:// scheme to file.managed.

This allows pillar data to be placed into a file without having to worry
about indentation in a sls file.
Moved pillar scheme logic to contents param.

Per discussion in issue #6508 applying a `pillar://` scheme to the
`source` parameter will be confusing because there is no parity with
other locations that use `source` and the most useful location for this
is the `file.managed` state.  In order to alleviate the problem, apply
the logic to the `contents` parameter, which is only supported in
`file.managed`.
Convert pillar:// scheme to contents_pillar variable

This builds off of pull req #6508, but discards the new URI scheme for a
dedicated argument to get the file contents from pillar.
Merge pull request #1 from terminalmage/file_managed_pillar_source_scheme

Convert pillar:// scheme to contents_pillar variable
Added tests for file.managed contents_pillar param
Merge pull request #6508 from rca/file_managed_pillar_source_scheme

Added pillar:// scheme to file.managed.