Property cannot reuse the name of another renamed property in the same mixed index

Hi
here is an issue related with mix index. Java client app connecting with janusgraph-0.5.3-gremlin-server, created a mix index(eg: edgeIndex) for several properties(eg: name, address), then rename name property to del_name, after that create "name" property again, and add the "name" property to mix index with error "Multiple entries with same key"

For confirmed bugs, please report:
- Version: 0.5.3
- Storage Backend: hbase 2.1.3
- Mixed Index Backend: elasticsearch 6.7.1
- Link to discussed bug:
- Expected Behavior:
- Current Behavior:
- Steps to Reproduce:
1. create property with mix index.
```
size = graph.getOpenTransactions().size();
for(i=0;i(RegularImmutableMap.java:70)
at com.google.common.collect.ImmutableMap$Builder.build(ImmutableMap.java:254)
at org.janusgraph.graphdb.database.IndexSerializer$IndexInfoRetriever$1.get(IndexSerializer.java:165)
at org.janusgraph.diskstorage.indexing.IndexTransaction.getIndexMutation(IndexTransaction.java:82)
at org.janusgraph.diskstorage.indexing.IndexTransaction.add(IndexTransaction.java:67)
at org.janusgraph.graphdb.database.StandardJanusGraph.prepareCommit(StandardJanusGraph.java:647)
at org.janusgraph.graphdb.database.StandardJanusGraph.commit(StandardJanusGraph.java:731)
at org.janusgraph.graphdb.transaction.StandardJanusGraphTx.commit(StandardJanusGraphTx.java:1438)
at org.janusgraph.graphdb.tinkerpop.JanusGraphBlueprintsGraph$GraphTransaction.doCommit(JanusGraphBlueprintsGraph.java:297)
at org.apache.tinkerpop.gremlin.structure.util.AbstractTransaction.commit(AbstractTransaction.java:104)
at org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor.onTraversalSuccess(TraversalOpProcessor.java:471)
at org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor.handleIterator(TraversalOpProcessor.java:603)
at org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor.lambda$iterateBytecodeTraversal$4(TraversalOpProcessor.java:411)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
88386919 [gremlin-server-exec-3] WARN org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor - Exception processing a Traversal on iteration for request [84e68f28-2fe0-4259-8eee-cfffc45e787c].
org.janusgraph.core.JanusGraphException: Could not commit transaction due to exception during persistence
at org.janusgraph.graphdb.transaction.StandardJanusGraphTx.commit(StandardJanusGraphTx.java:1449)
at org.janusgraph.graphdb.tinkerpop.JanusGraphBlueprintsGraph$GraphTransaction.doCommit(JanusGraphBlueprintsGraph.java:297)
at org.apache.tinkerpop.gremlin.structure.util.AbstractTransaction.commit(AbstractTransaction.java:104)
at org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor.onTraversalSuccess(TraversalOpProcessor.java:471)
at org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor.handleIterator(TraversalOpProcessor.java:603)
at org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor.lambda$iterateBytecodeTraversal$4(TraversalOpProcessor.java:411)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalArgumentException: Multiple entries with same key: name=org.janusgraph.diskstorage.indexing.StandardKeyInformation@4a1477cc and name=org.janusgraph.diskstorage.indexing.StandardKeyInformation@26dc5b3e
at com.google.common.collect.ImmutableMap.checkNoConflict(ImmutableMap.java:150)
at com.google.common.collect.RegularImmutableMap.checkNoConflictInBucket(RegularImmutableMap.java:104)
at com.google.common.collect.RegularImmutableMap.(RegularImmutableMap.java:70)
at com.google.common.collect.ImmutableMap$Builder.build(ImmutableMap.java:254)
at org.janusgraph.graphdb.database.IndexSerializer$IndexInfoRetriever$1.get(IndexSerializer.java:165)
at org.janusgraph.diskstorage.indexing.IndexTransaction.getIndexMutation(IndexTransaction.java:82)
at org.janusgraph.diskstorage.indexing.IndexTransaction.add(IndexTransaction.java:67)
at org.janusgraph.graphdb.database.StandardJanusGraph.prepareCommit(StandardJanusGraph.java:647)
at org.janusgraph.graphdb.database.StandardJanusGraph.commit(StandardJanusGraph.java:731)
at org.janusgraph.graphdb.transaction.StandardJanusGraphTx.commit(StandardJanusGraphTx.java:1438)
```

Start at org.janusgraph.graphdb.database.IndexSerializer.IndexInfoRetriever.get, reported at line 165, and reproduce the management sequence using the mixed index configuration described in the issue. Done means renaming a property and reusing its former name no longer produces duplicate-key entries when adding the property to the mixed index and committing.

Written by the indexing model from the issue text.