Problem description: multiple clicking on the "Import" button when trying to import a host or a template results in creation of multiple identical hosts, the only difference is host id, in such a way bypassing the validation for host name uniqueness.

Steps to reproduce:

1. Export a host (the more complex is its configuration, the better)
2. Open the exported file and change the name of the host.
3. Navigate to Configuration => Hosts and press "Import"
4. Select the previously modified export file and press "Import" button multiple times (as fast as You can).
5. Check Configuration => Hosts

Result: Multiple identical hosts were created.

Expected: Processing of multiple host/template import requests within such short period of time should be restricted - only 1 Host should've been created.

Example: