Create /etc/sysconfig/network if it doesn't exist

When the --hostname option is given to ipa-client-install, we
write HOSTNAME to /etc/sysconfig/network. When that file didn't exist,
the installer crashed.

Create the file if it doesn't exist and we need to write to it.

https://fedorahosted.org/freeipa/ticket/2840

ipapython/ipautil.py

@@ -991,13 +991,15 @@ $)''', re.VERBOSE)
 
     return old_values
 
-def backup_config_and_replace_variables(fstore, filepath, replacevars=dict(), appendvars=dict()):
+def backup_config_and_replace_variables(
+        fstore, filepath, replacevars=dict(), appendvars=dict()):
     """
     Take a key=value based configuration file, back up it, and
     write new version with certain values replaced or appended
 
     All (key,value) pairs from replacevars and appendvars that
     were not found in the configuration file, will be added there.
+    The file must exist before this function is called.
 
     It is responsibility of a caller to ensure that replacevars and
     appendvars do not overlap.

ipapython/platform/redhat.py

@@ -24,6 +24,8 @@ import os
 import stat
 import sys
 import socket
+import stat
+
 from ipapython import ipautil
 from ipapython.platform import base
 from ipalib import api
@@ -187,10 +189,18 @@ def backup_and_replace_hostname(fstore, statestore, hostname):
     except ipautil.CalledProcessError, e:
         print >>sys.stderr, "Failed to set this machine hostname to %s (%s)." % (hostname, str(e))
     replacevars = {'HOSTNAME':hostname}
-    old_values = ipautil.backup_config_and_replace_variables(fstore,
-                                                          "/etc/sysconfig/network",
-                                                          replacevars=replacevars)
+
+    filepath = '/etc/sysconfig/network'
+    if not os.path.exists(filepath):
+        # file doesn't exist; create it with correct ownership & mode
+        open(filepath, 'a').close()
+        os.chmod(filepath,
+            stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP | stat.S_IROTH)
+        os.chown(filepath, 0, 0)
+    old_values = ipautil.backup_config_and_replace_variables(
+        fstore, filepath, replacevars=replacevars)
     restore_context("/etc/sysconfig/network")
+
     if 'HOSTNAME' in old_values:
         statestore.backup_state('network', 'hostname', old_values['HOSTNAME'])
     else: