Allow pool 'alias' names

The following pool configuration would allow a pool to be aliased in POST
requests as 'centos-6-x86_64', 'centos-6-amd64', or 'centos-6-64':

````yaml
- name: 'centos-6-x86_64'
  alias: [ 'centos-6-amd64', 'centos-6-64' ]
  template: 'templates/centos-6-x86_64'
  folder: 'vmpooler/centos-6-x86_64'
  datastore: 'instance1'
  size: 5
````

The 'alias' configuration can be either a string or an array.

Note that even when requesting an alias, the pool's 'name' is returned in
the JSON response:

````
$ curl -d '{"centos-6-64":"1"}' --url vmpooler/api/v1/vm
````
````json
{
  "ok": true,
  "centos-6-x86_64": {
    "hostname": "cuna2qeahwlzji7"
  },
  "domain": "company.com"
}
````

vmpooler.yaml.example

@@ -188,6 +188,10 @@
 #     The name of the pool.
 #     (required)
 #
+#   - alias
+#     Other names this pool can be requested as.
+#     (optional)
+#
 #   - template
 #     The template or virtual machine target to spawn clones from.
 #     (required)
@@ -221,6 +225,7 @@
 
 :pools:
   - name: 'debian-7-i386'
+    alias: [ 'debian-7-32' ]
     template: 'Templates/debian-7-i386'
     folder: 'Pooled VMs/debian-7-i386'
     datastore: 'vmstorage'
@@ -228,6 +233,7 @@
     timeout: 15
     ready_ttl: 1440
   - name: 'debian-7-x86_64'
+    alias: [ 'debian-7-64', 'debian-7-amd64' ]
     template: 'Templates/debian-7-x86_64'
     folder: 'Pooled VMs/debian-7-x86_64'
     datastore: 'vmstorage'