Prevent excessive etelemetry pings

[effigies]

When etelemetry is down, nipype can spend excessive time re-trying instead of recording a failure mode.

On the one hand, this is a problem with the client. On the other, we should probably code defensively against bugs in the etelemetry client.

[mgxd]

nipype/nipype/interfaces/base/core.py

Lines 188 to 189 in 71c7a7d

	if BaseInterface._etelemetry_version_data is None:
	BaseInterface._etelemetry_version_data = check_latest_version()

I think the easiest thing to do would be to add a check if None is returned, and if so set BaseInterface._etelemetry_version_data to n/a or something equivalent