PYTHON-2737 Run Load Balancer test suite with Python 3.4 (#647)

Switch LB testing to amazon1-2018.

Author: ShaneHarvey

.evergreen/config.yml

@@ -2730,10 +2730,10 @@ buildvariants:
 
 - matrix_name: "load-balancer"
   matrix_spec:
-    platform: ubuntu-18.04
+    platform: awslinux
     mongodb-version: ["5.0", "latest"]
     auth-ssl: "*"
-    python-version: ["2.7", "3.5", "3.6", "3.7", "3.8", "3.9", "pypy", "pypy3.7"]
+    python-version: ["2.7", "3.4", "3.5", "3.6", "3.7", "3.8", "3.9", "pypy", "pypy3.5", "pypy3.7"]
     loadbalancer: "*"
   display_name: "Load Balancer ${platform} ${python-version} ${mongodb-version} ${auth-ssl}"
   tasks:

.evergreen/run-tests.sh

@@ -226,8 +226,8 @@ if [ -z "$GREEN_FRAMEWORK" ]; then
         $PYTHON -c "from bson import _cbson; from pymongo import _cmessage"
     fi
     if [ -n "$TEST_LOADBALANCER" ]; then
-        PY_MAJOR=$($PYTHON -c "import sys; sys.stdout.write(str(sys.version_info[0]))")
-        if [ "$PY_MAJOR" = "2" ]; then
+        IS_PRE_35=$(python -c "import sys; sys.stdout.write('1' if sys.version_info < (3, 5) else '0')")
+        if [ "$IS_PRE_35" = "1" ]; then
             RUNNER="unittest"
             RUNNER_ARGS=""
         else