RUBY-831 Catch OperationTimeout in client#active?
RUBY-831 Add default op timeout to MongoClient
RUBY-831 Update pool test to account for default op timeout on client
RUBY-831 Allow op timeout to be set to nil explicitly and update documentation for default value
Merge pull request #514 from estolfo/RUBY-831-client-active

RUBY-831 Return false from MongoClient#active? with OperationTimeout and set op timeout default