Run test cases in parallel

[Eskibear]

Now we have multiple test cases with a reasonable delay of 5s~10s. Run them in parallel will speed up the CI.

This PR:

• enables parallel mode
• set suite-level timeout instead of global

  custom client options
    ✔ should retry 2 times by default (5013ms)
    ✔ should override default retry options (10024ms)
    ✔ should retry on DNS failure (5005ms)


  request tracing
    ✔ should have correct user agent prefix (5004ms)
    ✔ should have request type in correlation-context header (5003ms)
    ✔ should have key vault tag in correlation-context header (5015ms)
    ✔ should detect env in correlation-context header (5011ms)
    ✔ should detect host type in correlation-context header (5002ms)
    ✔ should disable request tracing when AZURE_APP_CONFIGURATION_TRACING_DISABLED is true (10009ms)

Before

  29 passing (55s)

After

  29 passing (36s)