Changing default hash in file.py

Changed default hashtype in file.py to sha256.  This was not reading
the hash_type from the minion config.  FIPS doesnt allow md5 as a valid
hash type.

```
salt-call --versions
           Salt: 2014.1.7
         Python: 2.6.6 (r266:84292, Nov 21 2013, 10:50:32)
         Jinja2: 2.2.1
       M2Crypto: 0.20.2
 msgpack-python: 0.1.13
   msgpack-pure: Not Installed
       pycrypto: 2.0.1
         PyYAML: 3.10
          PyZMQ: 2.2.0.1
            ZMQ: 3.2.4
```

```
REDACTED ID :
----------
          ID: /etc/snmp/snmpd.conf
    Function: file.managed
      Result: False
     Comment: An exception occurred in this state: Traceback (most
recent call last):
                File "/usr/lib/python2.6/site-packages/salt/state.py",
line 1379, in call
                  **cdata['kwargs'])
                File
"/usr/lib/python2.6/site-packages/salt/states/file.py", line 1246, in
managed
                  **kwargs
                File
"/usr/lib/python2.6/site-packages/salt/modules/file.py", line 2363, in
check_managed
                  **kwargs)
                File
"/usr/lib/python2.6/site-packages/salt/modules/file.py", line 2106, in
get_managed
                  hsum = get_hash(sfn)
                File
"/usr/lib/python2.6/site-packages/salt/modules/file.py", line 424, in
get_hash
                  return salt.utils.get_hash(path, form, chunk_size)
                File
"/usr/lib/python2.6/site-packages/salt/utils/__init__.py", line 1468,
in get_hash
                  hash_obj = hash_type()
              ValueError: error:060800A3:digital envelope
routines:EVP_DigestInit_ex:disabled for fips

```


After the change:

```
REDACTED ID:
----------
          ID: /etc/snmp/snmpd.conf
    Function: file.managed
      Result: True
     Comment: File /etc/snmp/snmpd.conf updated
              diff: ---  
              +++  
              @@ -1,3 +1,3 @@
              REDACTED

```