{KeyVault} Modify random vault name prefix

[bim-msft]

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[bim-msft]

@jiasli Reduced the name prefix length to meet the rule and reran all tests according to your advice, please review it again.

[bim-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jiasli]

After live run KeyVaultCertificateDefaultPolicyScenarioTest, the recording yaml is removed. CI reports failure:

  File "/opt/hostedtoolcache/Python/3.6.10/x64/lib/python3.6/site-packages/azure/cli
    /command_modules/resource/custom.py", line 736, in create_resource_group
  ...
knack.util.CLIError: Please run 'az login' to setup account.

By looking into ResourceGroupPreparer then live_only_execute, see this line returns True:

azure-cli/src/azure-cli-testsdk/azure/cli/testsdk/preparers.py

Line 34 in 12f8746

if self.test_class_instance.in_recording:

Then find usage of in_recording reveals this line in azure_devtools.

self.in_recording = self.is_live or not os.path.exists(self.recording_file)

How it fails:

1. Because group create/delete commands are not recorded and there is no network traffic in the test body, after live run the yaml is not created
2. When running as recording, ReplayableTest gets is_live == False, but still thinks this is a live test because the yaml doesn't exists. In other words, the current design requires ResourceGroupPreparer to be paired with a recording yaml for the test to be treated as recording. Even if no --live or AZURE_TEST_RUN_LIVE is specified, lacking of yaml will still turn this test into a live test
3. The test is ran as live. This doesn't cause problem locally because az has been logged in, but in CI it has not.

To solve it, simply remove:

@ResourceGroupPreparer(name_prefix='cli_test_kv_cert_default_policy')