(#3146) - Adding pull replication performance tests

perf.basics.js - Add three tests. One does a pull replication against skimdb and is
disabled by default. The second and third tests test pull replication against a local
DB over the network. The difference between the tests is that one uses first generation
documents and the other uses second generation documents.

test/performance/utils.js - Fixed so that if iterations == 0 a test won't run and
also added a per test tear down functionality.

common-utils.js - Created this file to hold some, well, common utilities.

replication-test.js - Contains the pull replication test framework.

A huge thanks to daleharvey for taking the time to rework the content
in replication-test.js so it would be acceptable to the group!