Timeout when performing time sync during client install

We use ntpd now to sync time before fetching a TGT during client
install.  Unfortuantely, ntpd will hang forever if it is unable to
reach the NTP server.

This patch adds the ability for commands run via ipautil.run() to
have an optional timeout.  This capability is used by the NTP sync
code that is run during ipa-client-install.

Ticket: https://fedorahosted.org/freeipa/ticket/4842
Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>

ipapython/ipautil.py

@@ -249,7 +249,7 @@ def shell_quote(string):
 
 def run(args, stdin=None, raiseonerr=True,
         nolog=(), env=None, capture_output=True, skip_output=False, cwd=None,
-        runas=None):
+        runas=None, timeout=None):
     """
     Execute a command and return stdin, stdout and the process return code.
 
@@ -277,6 +277,8 @@ def run(args, stdin=None, raiseonerr=True,
     :param cwd: Current working directory
     :param runas: Name of a user that the command shold be run as. The spawned
         process will have both real and effective UID and GID set.
+    :param timeout: Timeout if the command hasn't returned within the specified
+        number of seconds.
     """
     p_in = None
     p_out = None
@@ -302,6 +304,11 @@ def run(args, stdin=None, raiseonerr=True,
         p_out = subprocess.PIPE
         p_err = subprocess.PIPE
 
+    if timeout:
+        # If a timeout was provided, use the timeout command
+        # to execute the requested command.
+        args[0:0] = [paths.BIN_TIMEOUT, str(timeout)]
+
     arg_string = nolog_replace(' '.join(shell_quote(a) for a in args), nolog)
     root_logger.debug('Starting external process')
     root_logger.debug('args=%s' % arg_string)
@@ -332,6 +339,9 @@ def run(args, stdin=None, raiseonerr=True,
         if skip_output:
             p_out.close()   # pylint: disable=E1103
 
+    if timeout and p.returncode == 124:
+        root_logger.debug('Process did not complete before timeout')
+
     root_logger.debug('Process finished, return code=%s', p.returncode)
 
     # The command and its output may include passwords that we don't want