[7.17] Handling exceptions on watcher reload (#105442)

[sakurai-youhei]

Backports the following commits to 7.17:

• Handling exceptions on watcher reload (Handling exceptions on watcher reload #105442)

[sakurai-youhei]

The build failed with the following errors:

> Task :x-pack:plugin:watcher:compileTestJava
/.../elasticsearch-pull-request/x-pack/plugin/watcher/src/test/java/org/elasticsearch/xpack/watcher/WatcherLifeCycleServiceTests.java:314: error: cannot find symbol
            .settings(settings(IndexVersion.current()).put(IndexMetadata.INDEX_FORMAT_SETTING.getKey(), 6)) // the internal index format,
                               ^
  symbol:   variable IndexVersion
  location: class WatcherLifeCycleServiceTests
/.../elasticsearch-pull-request/x-pack/plugin/watcher/src/test/java/org/elasticsearch/xpack/watcher/WatcherLifeCycleServiceTests.java:325: error: cannot find symbol
            .nodes(nodes.withMasterNodeId("node_1"))
                        ^
  symbol:   method withMasterNodeId(String)
  location: variable nodes of type DiscoveryNodes
/.../elasticsearch-pull-request/x-pack/plugin/watcher/src/test/java/org/elasticsearch/xpack/watcher/WatcherLifeCycleServiceTests.java:330: error: cannot find symbol
            .nodes(nodes.withMasterNodeId("node_2"))
                        ^
  symbol:   method withMasterNodeId(String)
  location: variable nodes of type DiscoveryNodes
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
3 errors

The first error indicates that the test depends on #94827, which is not back-ported to the 7.17 branch. But IndexVersion.current() could be rewritten with Version.CURRENT.

The second and third errors indicate that the test depends on #96836, which is also not back-ported to the 7.17. branch. But nodes.withMasterNodeId("X") could be rewritten with DiscoveryNodes.builder(nodes).masterNodeId("X").

[masseyke]

Thanks for updating it for V7 compatibility!