Unable to add new hosts to the cluster

Issue

• Adding new host to the environment immediately fails after approval of host.
• In engine.log traceback, a Null Pointer Exception is seen:

2018-04-13 22:23:16,271 ERROR [org.ovirt.engine.core.utils.hostinstall.VdsInstallerSSH] (pool-3-thread-49) Could not connect to server host.example.com: java.security.KeyStoreException: Failed to get certificate entry from key store: /etc/pki/ovirt-engine/.keystore/engine
        at org.ovirt.engine.core.utils.hostinstall.VdsInstallerSSH._doConnect(VdsInstallerSSH.java:143) [engine-utils.jar:]
        at org.ovirt.engine.core.utils.hostinstall.VdsInstallerSSH._doConnect(VdsInstallerSSH.java:78) [engine-utils.jar:]
        at org.ovirt.engine.core.utils.hostinstall.VdsInstallerSSH.connect(VdsInstallerSSH.java:286) [engine-utils.jar:]
        at org.ovirt.engine.core.utils.hostinstall.VdsInstallerSSH.connect(VdsInstallerSSH.java:257) [engine-utils.jar:]
        at org.ovirt.engine.core.bll.OVirtUpgrader.RunStage(OVirtUpgrader.java:41) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.VdsInstaller.Install(VdsInstaller.java:280) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.InstallVdsCommand.executeCommand(InstallVdsCommand.java:110) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.CommandBase.executeWithoutTransaction(CommandBase.java:876) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.CommandBase.executeActionInTransactionScope(CommandBase.java:973) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.CommandBase.runInTransaction(CommandBase.java:1372) [engine-bll.jar:]
        at org.ovirt.engine.core.utils.transaction.TransactionSupport.executeInSuppressed(TransactionSupport.java:168) [engine-utils.jar:]
        at org.ovirt.engine.core.utils.transaction.TransactionSupport.executeInScope(TransactionSupport.java:107) [engine-utils.jar:]
        at org.ovirt.engine.core.bll.CommandBase.execute(CommandBase.java:991) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.CommandBase.executeAction(CommandBase.java:291) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.MultipleActionsRunner.executeValidatedCommands(MultipleActionsRunner.java:182) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.MultipleActionsRunner.RunCommands(MultipleActionsRunner.java:162) [engine-bll.jar:]
        at org.ovirt.engine.core.bll.MultipleActionsRunner$1.run(MultipleActionsRunner.java:84) [engine-bll.jar:]
        at org.ovirt.engine.core.utils.threadpool.ThreadPoolUtil$InternalWrapperRunnable.run(ThreadPoolUtil.java:64) [engine-utils.jar:]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:473) [rt.jar:1.7.0_171]
        at java.util.concurrent.FutureTask.run(FutureTask.java:262) [rt.jar:1.7.0_171]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152) [rt.jar:1.7.0_171]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622) [rt.jar:1.7.0_171]
        at java.lang.Thread.run(Thread.java:748) [rt.jar:1.7.0_171]
Caused by: java.lang.NullPointerException: invalid null input
        at java.security.KeyStore$PrivateKeyEntry.<init>(KeyStore.java:460) [rt.jar:1.7.0_171]
        at java.security.KeyStore$PrivateKeyEntry.<init>(KeyStore.java:396) [rt.jar:1.7.0_171]
        at java.security.KeyStore$1.constructPrivateKeyEntry(KeyStore.java:196) [rt.jar:1.7.0_171]
        at sun.security.pkcs12.PKCS12KeyStore.engineGetEntry(PKCS12KeyStore.java:1223) [rt.jar:1.7.0_171]
        at sun.security.provider.KeyStoreDelegator.engineGetEntry(KeyStoreDelegator.java:172) [rt.jar:1.7.0_171]
        at sun.security.provider.JavaKeyStore$DualFormatJKS.engineGetEntry(JavaKeyStore.java:70) [rt.jar:1.7.0_171]
        at java.security.KeyStore.getEntry(KeyStore.java:1458) [rt.jar:1.7.0_171]
        at org.ovirt.engine.core.utils.hostinstall.VdsInstallerSSH._doConnect(VdsInstallerSSH.java:135) [engine-utils.jar:]