Set up CentOS 8 test farm tests (#8122)

Fixes #7420.

* Set up CentOS 8 test farm tests

* Don't add to apache2_targets until 7273 is resolved

* Start upgrade test from a version that works on centos 8

* remove when possible from targets

tests/letstest/apache2_targets.yaml

@@ -1,3 +1,5 @@
+# These images are located in us-east-1.
+
 targets:
   #-----------------------------------------------------------------------------
   #Ubuntu

tests/letstest/scripts/test_leauto_upgrades.sh

@@ -23,8 +23,8 @@ if command -v python && [ $(python -V 2>&1 | cut -d" " -f 2 | cut -d. -f1,2 | se
     INITIAL_VERSION="0.20.0"
     RUN_RHEL6_TESTS=1
 else
-    # 0.37.x is the oldest version of letsencrypt-auto that works on RHEL 8.
-    INITIAL_VERSION="0.37.1"
+    # 0.39.0 is the oldest version of letsencrypt-auto that works on CentOS 8.
+    INITIAL_VERSION="0.39.0"
 fi
 
 git checkout -f "v$INITIAL_VERSION" letsencrypt-auto

tests/letstest/targets.yaml

@@ -1,3 +1,5 @@
+# These images are located in us-east-1.
+
 targets:
   #-----------------------------------------------------------------------------
   #Ubuntu
@@ -85,3 +87,8 @@ targets:
       runcmd:
         - yum install -y epel-release
         - iptables -F
+  - ami: ami-01ca03df4a6012157
+    name: centos8
+    type: centos
+    virt: hvm
+    user: centos