Bugfix for Rerun button feature

[carlospzurita]

Description

Several issues have been reported with the recently merged PR https://github.com/etf-validator/etf-webapp/pull/196

• **Re-**running a test with the OGC Team Engine Test driver always results in a NullPointerException
• The rerun button does not work if the test object has been cleaned up and no longer exists.

This issue is intended as a mean to keep track of this problems, and a reference to a new Pull Request with a fix of this issues.

Operating systems and browser

• This issue affects both the frontend and the backend.

Steps to Reproduce

1. Create a new TestRun.
2. Go to the Test Reports tab, and click the rerun button.
3. Wait for the test to initialize.

Expected behavior: [Which behavior you expected to see instead and why.]

The test run initializes automatically, retrieving the provided TestObject from the ETF file system. If it is not available, it should request the TestObject again.

Actual behavior: [Describe the behavior you observed after following the steps]

• **Re-**running a test with the OGC Team Engine Test driver always results in a NullPointerException
• The rerun button does not work if the test object has been cleaned up and no longer exists.