SWIFT-1250 Add Atlas serverless connectivity tests (#677)

Author: kmahar

.evergreen/config.yml

@@ -179,6 +179,7 @@ functions:
           # DO NOT ECHO WITH XTRACE (which PREPARE_SHELL does)
           SWIFT_VERSION=${SWIFT_VERSION} ATLAS_REPL='${ATLAS_REPL}' ATLAS_SHRD='${ATLAS_SHRD}' ATLAS_FREE='${ATLAS_FREE}' ATLAS_TLS11='${ATLAS_TLS11}' ATLAS_TLS12='${ATLAS_TLS12}' \
           ATLAS_REPL_SRV='${ATLAS_REPL_SRV}' ATLAS_SHRD_SRV='${ATLAS_SHRD_SRV}' ATLAS_FREE_SRV='${ATLAS_FREE_SRV}' ATLAS_TLS11_SRV='${ATLAS_TLS11_SRV}' ATLAS_TLS12_SRV='${ATLAS_TLS12_SRV}' \
+          ATLAS_SERVERLESS='${ATLAS_SERVERLESS}' ATLAS_SERVERLESS_SRV='${ATLAS_SERVERLESS_SRV}' \
           sh ${PROJECT_DIRECTORY}/.evergreen/run-atlas-tests.sh
 
   "run serverless tests":

Sources/AtlasConnectivity/main.swift

@@ -1,11 +1,8 @@
 import Foundation
 import MongoSwiftSync
 
-private let configs = ["ATLAS_REPL", "ATLAS_SHRD", "ATLAS_FREE", "ATLAS_TLS11", "ATLAS_TLS12"]
+private let configs = ["ATLAS_REPL", "ATLAS_SHRD", "ATLAS_FREE", "ATLAS_TLS11", "ATLAS_TLS12", "ATLAS_SERVERLESS"]
 private let srvConfigs = configs.map { $0 + "_SRV" }
-/// Currently, almost all of the Atlas test instances are running 3.4 which does not support the new "hello" command.
-private let legacyHello = "ismaster"
-private let supportsHello = ["ATLAS_FREE", "ATLAS_FREE_SRV"]
 
 for config in configs + srvConfigs {
     print("Testing config \(config)... ", terminator: "")
@@ -17,13 +14,8 @@ for config in configs + srvConfigs {
 
     do {
         let client = try MongoClient(uri)
-        // run legacy hello command
         let db = client.db("test")
-        if supportsHello.contains(config) {
-            _ = try db.runCommand(["hello": 1])
-        } else {
-            _ = try db.runCommand([legacyHello: 1])
-        }
+        _ = try db.runCommand(["hello": 1])
 
         // findOne
         let coll = db.collection("test")