make cron module work on solaris

Cron on solaris do not take the same
set of option than vixie cron on linux, and
among the biggest difference, root cannot set
the crontab of a user directly from a file. Thus the
use of su to run the crontab command. Fix issue #4648

library/system/cron

@@ -144,6 +144,7 @@ EXAMPLES = '''
 import os
 import re
 import tempfile
+import platform
 
 CRONCMD = "/usr/bin/crontab"
 
@@ -345,21 +346,27 @@ class CronTab(object):
         """
         Returns the command line for reading a crontab
         """
-        return "%s -l %s" % (CRONCMD, self._user_execute())
+        user = ''
+        if self.user:
+            if platform.system() == 'SunOS':
+                return "su '%s' -c '%s -l'" % (self.user, CRONCMD)
+            else:
+                user = '-u %s' % self.user
+        return "%s %s %s" % (CRONCMD , user, '-l')
 
     def _write_execute(self, path):
         """
         Return the command line for writing a crontab
         """
-        return "%s %s %s" % (CRONCMD, self._user_execute(), path)
-
-    def _user_execute(self):
-        """
-        User command switches to append to the read and write commands.
-        """
+        user = ''
         if self.user:
-            return "%s %s" % ('-u', str(self.user))
-        return ''
+            if platform.system() == 'SunOS':
+                return "chown %s %s ; su '%s' -c '%s %s'" % (self.user, path, self.user, CRONCMD, path)
+            else:
+                user = '-u %s' % self.user
+        return "%s %s %s" % (CRONCMD , user, path)
+
+
 
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