TP: ensures that the DS view state is not reloaded until the DS update is complete

[mitchell852]

What does this PR (Pull Request) do?

• This PR fixes When a ds request is immediately fulfilled, the DS is not updating in TP #4269

Which Traffic Control components are affected by this PR?

• Traffic Portal

What is the best way to verify this PR?

• Turn dsRequests on in traffic_portal_properties.json
• Set the overrideRole in traffic_portal_properties.json (i.e. admin)
• Login to TP as a user with the overrideRole
• Update an existing delivery service. For example, change the routing name.
• Fulfill the ds request immediately
• Notice that the routing name has changed in the Delivery Service URL(s) section

If this is a bug fix, what versions of Traffic Control are affected?

• master (0c04aac)
• 4.0.0 (RC1)

The following criteria are ALL met by this PR

• This PR includes tests OR I have explained why tests are unnecessary
• This PR includes documentation OR I have explained why documentation is unnecessary
• This PR includes an update to CHANGELOG.md OR such an update is not necessary
• This PR includes any and all required license headers
• This PR ensures that database migration sequence is correct OR this PR does not include a database migration
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)