file module assumes it can do operations as salt user (root) then modify perms

Description of Issue/Question

file.managed is unable to write to a nfs mount

Setup

Create an nfs share, mount it on the minion.

file-on-nfs:
  file.managed:
    - name: /path/to/nfs/share/file-i-want-to-manage
    - source: salt://blah/files/file-i-want-to-manage.jinja
    - template: jinja
    - user: username
    - group: groupname
    - mode: 644

Steps to Reproduce Issue

1. Create nfs share on one VM (or just use one you have)
2. Mount nfs share on a second VM
3. Check you can write manually with touch /path/to/nfs/share/test
4. Try and manage file with salt

Errors

[INFO    ] Running state [/path/to/nfs/share/file-i-want-to-manage] at time 15:20:15.286419
[INFO    ] Executing state file.managed for [/path/to/nfs/share/file-i-want-to-manage]
[DEBUG   ] In saltenv 'base', looking at rel_path 'blah/files/file-i-want-to-manage.jinja' to resolve 'salt://blah/files/file-i-want-to-manage.jinja'
[DEBUG   ] In saltenv 'base', ** considering ** path /path/to/nfs/share/file-i-want-to-manage' to resolve 'salt://blah/files/file-i-want-to-manage.jinja'
[DEBUG   ] Fetching file from saltenv 'base', ** attempting ** 'salt://blah/files/file-i-want-to-manage.jinja'
[DEBUG   ] No dest file found
[INFO    ] Fetching file from saltenv 'base', ** done ** 'blah/files/file-i-want-to-manage.jinja'
[DEBUG   ] Jinja search path: ['/var/cache/salt/minion/files/base']
[DEBUG   ] Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/salt/states/file.py", line 2485, in managed
    **kwargs)
  File "/usr/lib/python2.7/site-packages/salt/modules/file.py", line 5051, in manage_file
    __opts__['cachedir'])
  File "/usr/lib/python2.7/site-packages/salt/utils/files.py", line 87, in copyfile
    tgt = mkstemp(prefix=bname, dir=dname)
  File "/usr/lib/python2.7/site-packages/salt/utils/files.py", line 51, in mkstemp
    return salt.utils.mkstemp(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/salt/utils/__init__.py", line 3491, in mkstemp
    fd_, fpath = tempfile.mkstemp(*args, **kwargs)
  File "/usr/lib64/python2.7/tempfile.py", line 304, in mkstemp
    return _mkstemp_inner(dir, prefix, suffix, flags)
  File "/usr/lib64/python2.7/tempfile.py", line 239, in _mkstemp_inner
    fd = _os.open(file, flags, 0600)
OSError: [Errno 13] Permission denied: '/path/to/nfs/share/file-i-want-to-manageiAn_w1'

[ERROR   ] Unable to manage file: [Errno 13] Permission denied: /path/to/nfs/share/file-i-want-to-manageAn_w1'
[INFO    ] Completed state [/path/to/nfs/share/file-i-want-to-manage] at time 15:20:15.327657 duration_in_ms=41.237

nfs mount details: 192.168.10.13:/nfs/blah on /path/to/nfs/share type nfs4 (rw,noatime,vers=4.1,rsize=32768,wsize=32768,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.10.14,lookupcache=pos,local_lock=none,addr=192.168.10.13)

To confirm, I am able to read/write/delete files on the nfs share with the user specified manually, it is only Salt unable to write.

Versions Report

Salt Version:
           Salt: 2017.7.0-n/a-5d719a2
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: Not Installed
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.7.2
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.4.8
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 2.7.5 (default, Aug  4 2017, 00:39:18)
   python-gnupg: Not Installed
         PyYAML: 3.11
          PyZMQ: 15.3.0
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 4.1.4
 
System Versions:
           dist: centos 7.4.1708 Core
         locale: UTF-8
        machine: x86_64
        release: 3.10.0-693.5.2.el7.x86_64
         system: Linux
        version: CentOS Linux 7.4.1708 Core

Start in salt/states/file.py and salt/modules/file.py, following the traceback into salt/utils/files.py and salt/utils/init.py. Reproduce file.managed against the described NFS mount, compare Salt's temporary-file handling with the successful manual operation, and verify that the managed file can be written with the requested user, group, and mode.