This patch does the following things:
1. The return value of cmdSchedInfoUpdate() can be -1, 0 and 1. So the
   type of return value should be int not bool.(This function is not a
   entry of a virsh command, but the name of this function likes cmdXXX)

2. The type of cmdSchedinfo()'s, cmdFreecell()'s, cmdPoolList()'s and
   cmdVolList()'s return value is bool not int, so change the type of
   variable ret_val, func_ret and functionReturn.

3. Add a variable functionReturn for cmdMigrate(), cmdAttachInterface(),
   cmdDetachInterface(), cmdAttachDisk() and cmdDetachDisk() to save the
   return value.

4. Change the type of variable ret in the function cmdAttachDevice(),
   cmdDetachDevice(), cmdUpdateDevice(), cmdAttachInterface(),
   cmdDetachInterface(), cmdAttachDisk() and cmdDetachDisk() to int, as
   we use it to save the return value of virXXX() and the type of virXXX()'s
   return value is int not bool.

5. Do some cleanup when virBuff.error is 1.

The bug 1-4 were introduced by commit b56fa5bb.