Refactored connection pool (#913)

* Refactored ConnectionPool
- Created BaseConnectionPool class
- Created CloudConnectionPool
- connection pool updates are immutable
- resurrect now happens inside getConnection()

* Rewritten connection pool(s) type definitions

* Updated test

* Fixed test

* Fix if check

* Removed old files

* Improve code coverage

* Updated license header

* Fix if check

* Improve code coverage

* Updated coverage script

lib/Transport.js

@@ -314,10 +314,12 @@ class Transport {
     if (this._sniffEnabled === true && now > this._nextSniff) {
       this.sniff({ reason: Transport.sniffReasons.SNIFF_INTERVAL, requestId: opts.requestId })
     }
-    this.connectionPool.resurrect({ now, requestId: opts.requestId, name: this.name })
     return this.connectionPool.getConnection({
       filter: this.nodeFilter,
-      selector: this.nodeSelector
+      selector: this.nodeSelector,
+      requestId: opts.requestId,
+      name: this.name,
+      now
     })
   }