MINOR: Fix bug encountered when restoring RUN SCRIPT command.

[vcrfxia]

Description

Currently, if you execute a RUN SCRIPT where the script contains a persistent query, then try to restart the KSQL server, the server will fail to restart. This happens because recent changes we introduced to the recovery logic result in the server attempting to start the persistent query created by the RUN SCRIPT twice, resulting in the following error:

[2018-12-12 19:59:46,205] ERROR Failed to start KSQL (io.confluent.ksql.rest.server.KsqlServerMain:47)
java.lang.IllegalStateException: Can only set StateListener in CREATED state. Current state is: REBALANCING
    at org.apache.kafka.streams.KafkaStreams.setStateListener(KafkaStreams.java:332)
    at java.util.Optional.ifPresent(Optional.java:159)
    at io.confluent.ksql.util.QueryMetadata.start(QueryMetadata.java:183)
    at java.util.ArrayList.forEach(ArrayList.java:1257)
    at java.util.Collections$UnmodifiableCollection.forEach(Collections.java:1080)
    at io.confluent.ksql.rest.server.computation.StatementExecutor.handleRestoration(StatementExecutor.java:104)
    at io.confluent.ksql.rest.server.computation.CommandRunner.processPriorCommands(CommandRunner.java:89)
    at io.confluent.ksql.rest.server.KsqlRestApplication.buildApplication(KsqlRestApplication.java:384)
    at io.confluent.ksql.rest.server.KsqlServerMain.createExecutable(KsqlServerMain.java:82)
    at io.confluent.ksql.rest.server.KsqlServerMain.main(KsqlServerMain.java:44)

The fix is simple: only start RUN SCRIPT queries once when recovering.

Testing done

Manual testing done. Added unit test.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[apurvam]

LGTM, thanks for digging into this, and thanks for the patch!

[hjafarpour]

LGTM.