dns: add CNAME to possible search types (#1143)

centreon-plugins/apps/protocols/dns/lib/dns.pm

@@ -32,6 +32,7 @@ my %map_search_field = (
     NS => 'nsdname',
     A => 'address',
     PTR => 'name',
+    CNAME => 'cname',
 );
 
 sub search {

centreon-plugins/apps/protocols/dns/mode/request.pm

@@ -167,7 +167,7 @@ Set the search value (required).
 
 =item B<--search-type>
 
-Set the search type. Can be: 'MX', 'SOA', 'NS', 'A' or 'PTR'.
+Set the search type. Can be: 'MX', 'SOA', 'NS', 'A', 'CNAME' or 'PTR'.
 'A' or 'PTR' is used by default (depends if an IP or not).
 
 =item B<--expected-answer>