Added `maxPollRetries` setting and poll retry logic:

SauceLabs' status endpoint fails intermittently causing the test run to fail because of connection issues and not because of failing tests. The `maxPollRetries` setting tell the job to not fail immediately but be able to recover within N retries.
Updated README
Merge pull request #175 from marioestrada/max-poll-retries

Added `maxPollRetries` setting and poll retry logic: