Dataflow runner throws unclear exception when credential is not set properly

```

Caused by: java.lang.IllegalArgumentException: Error constructing default value for gcpTempLocation:
tempLocation is not a valid GCS path, gs://....
at org.apache.beam.sdk.extensions.gcp.options.GcpOptions$GcpTempLocationFactory.create(GcpOptions.java:319)

at org.apache.beam.sdk.extensions.gcp.options.GcpOptions$GcpTempLocationFactory.create(GcpOptions.java:297)

at org.apache.beam.sdk.options.ProxyInvocationHandler.returnDefaultHelper(ProxyInvocationHandler.java:605)

at org.apache.beam.sdk.options.ProxyInvocationHandler.getDefault(ProxyInvocationHandler.java:546)

at org.apache.beam.sdk.options.ProxyInvocationHandler.invoke(ProxyInvocationHandler.java:171)

at com.sun.proxy.$Proxy25.getGcpTempLocation(Unknown Source)
at org.apache.beam.runners.dataflow.DataflowRunner.fromOptions(DataflowRunner.java:278)

... 16 more
Caused by: java.lang.IllegalArgumentException: Output path does not exist or is
not writeable: gs://...

```

When user submits pipeline but the google cloud credential was not set properly in the terminal, the runner throw above exception, which is confusing. 

Proper exception regarding credential issues should be more clear for user to troubleshoot.

Imported from Jira [BEAM-12718](https://issues.apache.org/jira/browse/BEAM-12718). Original Jira may contain additional context.
Reported by: yichi.