Description of problem:
When granting a booth ticket by running 'pcs booth ticket grant' command on a booth arbitrator, a site the ticket is being granted to must be specified. When no site is specified, pcs should exit with an error. Currently, the error reported by pcs in this case is confusing and doesn't help in any way to figure out how to proceed.

Version-Release number of selected component (if applicable):
pcs-0.10

How reproducible:
always

Steps to Reproduce:
1. Have two clusters (clusterA: nodeA1, nodeA2; clusterB: nodeB1, nodeB2) and an additional node to serve as an arbitrator.

1. create and distribute booth config
   2. [nodeA1]# pcs booth setup sites {ipA} {ipB} arbitrators {ipArbitrator}
   3. [nodeA1]# pcs booth ticket add ticket1
   4. [nodeA1]# pcs booth sync
   5. [nodeB1]# pcs booth pull nodeA1 && pcs booth sync
   6. [arbitrator]# pcs booth pull nodeA1
   # start booth
   7. [arbitrator]# pcs booth enable && pcs booth start
   8. [nodeA1]# pcs booth create ip {ipA}

   9. [nodeB1]# pcs booth create ip

   {ipB}
2. grant a ticket
   10. [arbitrator]# pcs booth ticket grant ticket1

Actual results:
[arbitrator]# pcs booth ticket grant ticket1
Error: unable to get cib
[arbitrator]# pcs booth ticket revoke ticket1
Error: unable to get cib

Expected results:
pcs should explain that a booth site must be specified when granting tickets from an arbitrator