Fix tests broken because future not completed during cleanup (#121782) (#121820)

A future.actionGet was missing from the delete pipeline action execution in the test cleanup, causing all tests to fail intermittently. Also replace actionGet with safeGet.

(cherry picked from commit 0f6b80a)

# Conflicts:
#	muted-tests.yml
#	x-pack/plugin/migrate/src/internalClusterTest/java/org/elasticsearch/xpack/migrate/action/ReindexDatastreamIndexTransportActionIT.java

Author: parkertimmins

muted-tests.yml

@@ -350,9 +350,6 @@ tests:
 - class: org.elasticsearch.reservedstate.service.RepositoriesFileSettingsIT
   method: testSettingsApplied
   issue: https://github.com/elastic/elasticsearch/issues/116694
-- class: org.elasticsearch.xpack.test.rest.XPackRestIT
-  method: test {p0=migrate/20_reindex_status/Test Reindex With Existing Data Stream}
-  issue: https://github.com/elastic/elasticsearch/issues/118576
 - class: org.elasticsearch.discovery.ec2.DiscoveryEc2AvailabilityZoneAttributeNoImdsIT
   method: testAvailabilityZoneAttribute
   issue: https://github.com/elastic/elasticsearch/issues/118564
@@ -518,9 +515,6 @@ tests:
 - class: org.elasticsearch.xpack.ml.integration.ClassificationIT
   method: testWithOnlyTrainingRowsAndTrainingPercentIsHundred
   issue: https://github.com/elastic/elasticsearch/issues/121368
-- class: org.elasticsearch.xpack.migrate.action.ReindexDatastreamIndexTransportActionIT
-  method: testFailIfMetadataBlockSet
-  issue: https://github.com/elastic/elasticsearch/issues/121774
 - class: org.elasticsearch.xpack.ml.packageloader.action.ModelLoaderUtilsTests
   method: testSplitIntoRanges
   issue: https://github.com/elastic/elasticsearch/issues/121799