[AMQ7, shared store] Backup broker does not activate after shared store is reconnected

Issue

• if the shared store disk (networked storage) is disconnected from the master and slave brokers, the slave broker does not become "live" when the connection to the disk is reestablished. It remains as a "backup" even though the master broker has failed.

• The slave broker does not try to reconnect to the store after it experiences the following error (due to the disk being not available)

05:50:57,896 ERROR [org.apache.activemq.artemis.core.server] (AMQ119000: Activation for server ActiveMQServerImpl::serverUUID=836c9b1e-f067-11e7-8763-001b21862475) AMQ224000: Failure in initialisation: java.io.IOException: Input/output error
    at sun.nio.ch.FileDispatcherImpl.lock0(Native Method) [rt.jar:1.8.0_151]
    at sun.nio.ch.FileDispatcherImpl.lock(FileDispatcherImpl.java:90) [rt.jar:1.8.0_151]
    at sun.nio.ch.FileChannelImpl.tryLock(FileChannelImpl.java:1115) [rt.jar:1.8.0_151]
    at org.apache.activemq.artemis.core.server.impl.FileLockNodeManager.tryLock(FileLockNodeManager.java:299) [artemis-server-1.5.5.008-redhat-1.jar:1.5.5.008-redhat-1]
    at org.apache.activemq.artemis.core.server.impl.FileLockNodeManager.lock(FileLockNodeManager.java:316) [artemis-server-1.5.5.008-redhat-1.jar:1.5.5.008-redhat-1]
    at org.apache.activemq.artemis.core.server.impl.FileLockNodeManager.awaitLiveNode(FileLockNodeManager.java:127) [artemis-server-1.5.5.008-redhat-1.jar:1.5.5.008-redhat-1]
    at org.apache.activemq.artemis.core.server.impl.SharedStoreBackupActivation.run(SharedStoreBackupActivation.java:77) [artemis-server-1.5.5.008-redhat-1.jar:1.5.5.008-redhat-1]
    at org.apache.activemq.artemis.core.server.impl.ActiveMQServerImpl$ActivationThread.run(ActiveMQServerImpl.java:2496) [artemis-server-1.5.5.008-redhat-1.jar:1.5.5.008-redhat-1]