RUBY-472 internal read_preference -> read

It doesn't make sense to call this variable read_preference internally
because its actually just the mode portion of the read preference. We
should probably change to mode at a later date but we'll keep it at
read because its easy to understand given the opt key is read.
minor: go from instance to local vars in refresh test
minor: make replica_set_startup more strict

It's necessary to call replSetGetStatus on each member of the set and
make sure they all agree that the set is up instead of relying on one
member.
minor: prune unnecesary duplicate tests

this is already tested by the client tests -- no need to repeat
RUBY-472 move #near_pool and #select_pool into module
minor: flip some logic to get rid of !(nots)
minor: should referece function instead of instance var
minor: improvements to client_test
RUBY-472 move new shared functionality into client
minor: whitespace ocd
RUBY-472 make rs set health easier to grok
minor: secondaries should be a set
RUBY-472 support sending $readPreference to mongos
RUBY-472 fix for sharded cluster test under 1.8.7
RUBY-472 actually test different things
RUBY-472 minor fixes
RUBY-472 fix for 1.8.7 selector order
RUBY-472 refactor set_config
RUBY-476 add test for find_and_modify with :read => :secondary
minor: various tweaks to cluster test tool