Increase test coverage to 95%

[avital]

Goal: 95% or more.

• Test passing mongo string into ShareDbMongo constructor
• Test the "flush pending connection" logic
• Test $count
• Test the logic in queryPollDoc that modified Mongo queries with _id
• Test the mongoPoll and pollDelay options
• Test $skip and $limit

[coveralls]

Coverage increased (+3.3%) to 89.729% when pulling c02e64f on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+3.3%) to 89.729% when pulling 27e4cb9 on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+4.07%) to 90.504% when pulling 6afec55 on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+5.4%) to 91.86% when pulling 5200c39 on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage decreased (-69.4%) to 17.054% when pulling 5f4a75b on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+5.4%) to 91.86% when pulling dca0b52 on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+6.4%) to 92.829% when pulling 3be0a04 on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+6.4%) to 92.829% when pulling 6311782 on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+8.5%) to 94.961% when pulling 24d9a9a on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+8.9%) to 95.349% when pulling e5690e2 on avital:more-coverage into 89dfa91 on share:master.

[avital]

We passed 95%. And an additional 0.6% from #25.

@nateps: This is ready for review now. Please let me know if there are any other particular parts you think are important to test. (It seemed tricky to write robust tests for all cases in the "There is no snapshot currently" section in filterOps).

[avital]

(Sadly the "db client query subscribe pollDebounce option reduces subsequent poll interval" test is still flaky. I'll look into that)

[coveralls]

Coverage increased (+8.9%) to 95.349% when pulling 5b62228 on avital:more-coverage into 89dfa91 on share:master.

[coveralls]

Coverage increased (+8.9%) to 95.349% when pulling 125f1ca on avital:more-coverage into 89dfa91 on share:master.

[avital]

forEach instead of IIFE

[coveralls]

Coverage increased (+8.6%) to 92.893% when pulling 222a60e on avital:more-coverage into c2131b5 on share:master.

[coveralls]

Coverage increased (+8.6%) to 92.893% when pulling 41e1c44 on avital:more-coverage into c2131b5 on share:master.