Bad value [first.middle.lastname]: Only hyphens (-), underscores (_), lowercase characters, and numbers are allowed.

The error originates from gcloud, however I don't have this issue when using gcloud myself.
I believe PKB is using my email address to label something, and it isn't allowed because of the periods.

My email address is "first.middle.lastname@company.com" and I can not remove the periods from my company email.

```Exception running benchmark
Traceback (most recent call last):
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/pkb.py", line 1314, in RunBenchmarkTask
RunBenchmark(spec_for_run, collector)
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/pkb.py", line 1091, in RunBenchmark
DoProvisionPhase(spec, detailed_timer)
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/pkb.py", line 762, in DoProvisionPhase
spec.Provision()
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/benchmark_spec.py", line 712, in Provision
vm_util.RunThreaded(
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/background_tasks.py", line 647, in RunThreaded
return RunParallelThreads(target_arg_tuples,
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/background_tasks.py", line 582, in RunParallelThreads
return _RunParallelTasks(
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/background_tasks.py", line 556, in _RunParallelTasks
raise parallel_exception_class(
perfkitbenchmarker.errors.VmUtil.ThreadException: The following exceptions occurred during parallel execution:
Exception occurred while calling CreateAndBootVm():
Traceback (most recent call last):
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/background_tasks.py", line 252, in Run
self.return_value = self.target(*self.args, **self.kwargs)
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/benchmark_spec.py", line 944, in CreateAndBootVm
vm.Create()
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/resource.py", line 355, in Create
self._CreateResource()
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/vm_util.py", line 261, in WrappedFunction
return f(*args, **kwargs)
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/resource.py", line 262, in _CreateResource
self._Create()
File "/home/first.middle.lastname/PerfKitBenchmarker/perfkitbenchmarker/providers/gcp/gce_virtual_machine.py", line 743, in _Create
raise errors.Resource.CreationError(
perfkitbenchmarker.errors.Resource.CreationError: Failed to create VM: ERROR: (gcloud.compute.instances.create) argument --labels: Bad value [first.middle.lastname]: Only hyphens (-), underscores (_), lowercase characters, and numbers are allowed. International characters are allowed.
```

The command I am running is:
`
./pkb.py --benchmarks=cluster_boot --machine_type=f1-micro --zones=us-central1-f --run_stage=provision,prepare,run
`