prow.sh: fix hostpath driver version check

The previous logic failed for canary jobs, those also deploy a recent
driver. Instead of guessing what driver gets installed based on job
parameters, check what really runs in the cluster and base the
decision on that.

We only need to maintain this blacklist for 1.0.x until we replace it
with 1.1.0, then this entire hostpath_supports_block can be removed.

prow.sh

@@ -619,18 +619,18 @@ install_sanity () (
 
 # Whether the hostpath driver supports raw block devices depends on which version
 # we are testing. It would be much nicer if we could determine that by querying the
-# installed driver.
+# installed driver's capabilities instead of having to do a version check.
 hostpath_supports_block () {
-    if [ -e "cmd/hostpathplugin" ] && ${CSI_PROW_BUILD_JOB}; then
-        # The assumption is that if we build the hostpath driver, then it is
-        # a current version with support.
-        echo true
-        return
-    fi
-
-    case "${CSI_PROW_DEPLOYMENT}" in kubernetes-1.13) echo false;; # wasn't supported and probably won't be backported
-                                      *) echo true;; # probably all other deployments have a recent driver
-    esac
+    local result
+    result="$(docker exec csi-prow-control-plane docker image ls --format='{{.Repository}} {{.Tag}} {{.ID}}' | grep hostpath | while read -r repo tag id; do
+        if [ "$tag" == "v1.0.1" ]; then
+            # Old version because the revision label is missing: didn't have support yet.
+            echo "false"
+            return
+        fi
+    done)"
+    # If not set, then it must be a newer driver with support.
+    echo "${result:-true}"
 }
 
 # Captures pod output while running some other command.