Dell Storage Center: Add retries to API calls

Dell Storage Center: Add retries to API calls

In heavily loaded networks we have seen some cases
of temporary ConnectionErrors when making REST API
calls. There are usually successful calls just prior
and immediately after these failures, so it appears
to be a transient condition.

This patch utilizes the recently merged retry decorator
to add some retry handling to the REST API calls when
this condition is encountered.

With a test script looping through repeatedly running
CI against this first patch I was able to validate
that it addresses the issue. Out of 20 runs, a full
2/3 of the tests passed showing that the retry was
used. These test runs would have failed without the
retry.

The output from these test runs can be viewed here:

http://oslogs.compellent.com/?C=N;O=D

Pertinent results are dell-sc-iscsi-1554792015-12*

Once merged we should be able to enable full third
party CI testing with some expectation of reliable
results.

Closes-Bug: 1422742
Change-Id: I1279a7696068aee534498bb18f4f6b4fbb7a33d5