`file.managed` fails in `/proc`

Description of Issue

Attempts to set ip_forward flag in /proc fail using file.managed.

Setup

/proc/sys/net/ipv4/ip_forward:
  file.managed:
    - contents: |
        1

Steps to Reproduce Issue

Run the state. See the issue:

  ID: /proc/sys/net/ipv4/ip_forward
                  Function: file.managed
                    Result: False
                   Comment: Failed to commit change: [Errno 2] No such file or directory: '/proc/sys/net/ipv4/ip_forwardau_x0ze7'
                   Started: 20:47:26.891354
                  Duration: 23.426 ms
                   Changes:   
                            ----------
                            diff:
                                --- 
                                +++ 
                                @@ -1 +1 @@
                                -0
                                +1

Versions Report

Salt Version:
           Salt: 2019.2.2-3-g71e0088
 
Dependency Versions:
           cffi: 1.13.0
       cherrypy: Not Installed
       dateutil: 2.8.0
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
          ioflo: Not Installed
         Jinja2: 2.10.3
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.6.2
   mysql-python: Not Installed
      pycparser: 2.19
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.6.8 (default, Oct  7 2019, 12:59:55)
   python-gnupg: Not Installed
         PyYAML: 3.13
          PyZMQ: 18.1.0
           RAET: Not Installed
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.3.2
 
System Versions:
           dist: Ubuntu 18.04 bionic
         locale: UTF-8
        machine: x86_64
        release: 4.15.0-65-generic
         system: Linux
        version: Ubuntu 18.04 bionic
 

Start from the file.managed entry point and reproduce the state against /proc/sys/net/ipv4/ip_forward on Ubuntu/Linux. Investigate why the change uses a temporary path that procfs cannot create; done means file.managed can set ip_forward successfully without the reported temporary-file error.