Try to amend TestAccVcdNsxtDynamicSecurityGroupVdcGroupCriteriaWithVm

[adambarreiro]

This PR tries to solve the following test failure that is intermittent and difficult to catch:

=== RUN   TestAccVcdNsxtDynamicSecurityGroupVdcGroupCriteriaWithVms
    resource_vcd_nsxt_dynamic_security_group_test.go:438: Step 2/4 error: Error running post-apply plan: exit status 1
        
        Error: [nsxt dynamic security group data source read] error getting NSX-T dynamic security group: could not find NSX-T Firewall Group with name 'TestAccVcdNsxtDynamicSecurityGroupVdcGroupCriteriaWithVms-group2': error getting all pages for endpoint https://my-super-duper-vcd.company.com/cloudapi/1.0.0/firewallGroups/summaries: error in HTTP GET request: BAD_REQUEST - Cannot parse the supplied filter: typeValue==VM_CRITERIA;ownerRef.id==urn:vcloud:vdcGroup:65aff636-d9ef-4aca-b4ca-3132f6346fde;name==TestAccVcdNsxtDynamicSecurityGroupVdcGroupCriteriaWithVms-group2
        
          with data.vcd_nsxt_dynamic_security_group.group2,
          on terraform_plugin_test.tf line 164, in data "vcd_nsxt_dynamic_security_group" "group2":
         164: data "vcd_nsxt_dynamic_security_group" "group2" {
        
--- FAIL: TestAccVcdNsxtDynamicSecurityGroupVdcGroupCriteriaWithVms (156.58s)

The hypothesis is that the name could be too long and sometimes it could break the VCD API filter, but this is not 100% sure.
This PR changes the used name to shorter ones, like
name==DSGVdcGroupCritWithVms-2

We should check in future whether this test continues to fail despite this change.