Fix createCollection tests for 2.5.x

Use 4096 for capped collection size instead of 100, since server rounds up to the nearest extent anyway. As of https://jira.mongodb.org/browse/SERVER-12794, the actual storage size is reported, so we can use and expect 4096.

Additionally, use dump_these_keys() to print collection options, so we don't need to worry about extra options or their order.
Do not test with a 2dsphere sparse index

Since we still test against 2.2.x, creating a 2dsphere index here would result in an index being created with an invalid plugin name.

This case also caused problems with other, unrelated tests that created 2d indexes, as they would fail with the following error: "Found pre-existing index { v: 1, key: { b: "2dsphere" }, name: "b_2dsphere", ns: "test.col1", sparse: true, 2dsphereIndexVersion: 2 } with invalid type '2dsphere'. Disallowing creation of new index type '2d'."