Added validate option to lineinfile

The validate option is constructed similarly to the template command's
validate option. TestRunner.py has been updated to include two new
tests, one for passing and one for failing validation.

files/lineinfile

@@ -107,6 +107,13 @@ options:
      description:
        - Create a backup file including the timestamp information so you can
          get the original file back if you somehow clobbered it incorrectly.
+  validate:
+     required: false
+     description:
+       - validation to run before copying into place
+     required: false
+     default: None
+     version_added: "1.4"
   others:
      description:
        - All arguments accepted by the M(file) module also work here.
@@ -128,6 +135,9 @@ EXAMPLES = r"""
 - lineinfile: "dest=/etc/sudoers state=present regexp='^%wheel' line='%wheel ALL=(ALL) NOPASSWD: ALL'"
 
 - lineinfile: dest=/opt/jboss-as/bin/standalone.conf regexp='^(.*)Xms(\d+)m(.*)$' line='\1Xms${xms}m\3' backrefs=yes
+
+# Validate a the sudoers file before saving
+- lineinfile: dest=/etc/sudoers state=present regexp='^%ADMIN ALL\=' line='%ADMIN ALL=(ALL) NOPASSWD:ALL' validate='visudo -cf %s'
 """
 
 def write_changes(module,lines,dest):
@@ -137,7 +147,16 @@ def write_changes(module,lines,dest):
     f.writelines(lines)
     f.close()
 
-    module.atomic_move(tmpfile, dest)
+    validate = module.params.get('validate', None)
+    valid = not validate
+    if validate:
+        (rc, out, err) = module.run_command(validate % tmpfile)
+        valid = rc == 0
+        if rc != 0:
+            module.fail_json(msg='failed to validate: '
+                                 'rc:%s error:%s' % (rc,err))
+    if valid:
+        module.atomic_move(tmpfile, dest)
 
 def check_file_attrs(module, changed, message):
 
@@ -167,8 +186,6 @@ def present(module, dest, regexp, line, insertafter, insertbefore, create,
         lines = f.readlines()
         f.close()
 
-    msg = ""
-
     mre = re.compile(regexp)
 
     if insertafter not in (None, 'BOF', 'EOF'):
@@ -289,6 +306,7 @@ def main():
             backrefs=dict(default=False, type='bool'),
             create=dict(default=False, type='bool'),
             backup=dict(default=False, type='bool'),
+            validate=dict(default=None, type='str'),
         ),
         mutually_exclusive=[['insertbefore', 'insertafter']],
         add_file_common_args=True,