graph variable values do not support list

Tested : janus 0.2.0
Documented by tinkerpop:
[tinkerpop doc](http://tinkerpop.apache.org/docs/current/reference/)
doc section 'Graph Variables'

gremlin> graph
==>standardjanusgraph[cql:[127.0.0.1]]
gremlin> graph.variables().set('systemAdmins',['stephen','peter','pavel'])
Graph variable value [[stephen, peter, pavel]] is of type class java.util.ArrayList is not supported
Type ':help' or ':h' for help.
Display stack trace? [yN]y
java.lang.UnsupportedOperationException: Graph variable value [[stephen, peter, pavel]] is of type class java.util.ArrayList is not supported
at org.apache.tinkerpop.gremlin.structure.Graph$Variables$Exceptions.dataTypeOfVariableValueNotSupported(Graph.java:399)
at org.apache.tinkerpop.gremlin.structure.Graph$Variables$Exceptions.dataTypeOfVariableValueNotSupported(Graph.java:395)
at org.janusgraph.diskstorage.configuration.backend.KCVSConfiguration.object2StaticBuffer(KCVSConfiguration.java:255)
at org.janusgraph.diskstorage.configuration.backend.KCVSConfiguration.set(KCVSConfiguration.java:140)
at org.janusgraph.diskstorage.configuration.backend.KCVSConfiguration.set(KCVSConfiguration.java:130)
at org.janusgraph.graphdb.tinkerpop.JanusGraphVariables.set(JanusGraphVariables.java:56)
at org.apache.tinkerpop.gremlin.structure.Graph$Variables$set.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:133)
at groovysh_evaluate.run(groovysh_evaluate:3)
at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:232)
at org.codehaus.groovy.tools.shell.Interpreter.evaluate(Interpreter.groovy:70)
at org.codehaus.groovy.tools.shell.Groovysh.execute(Groovysh.groovy:191)
at org.apache.tinkerpop.gremlin.console.GremlinGroovysh.super$3$execute(GremlinGroovysh.groovy)
at sun.reflect.GeneratedMethodAccessor14.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:132)
at org.apache.tinkerpop.gremlin.console.GremlinGroovysh.execute(GremlinGroovysh.groovy:72)
at org.codehaus.groovy.tools.shell.Shell.leftShift(Shell.groovy:122)
at org.codehaus.groovy.tools.shell.ShellRunner.work(ShellRunner.groovy:95)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.super$2$work(InteractiveShellRunner.groovy)
at sun.reflect.GeneratedMethodAccessor55.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:132)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuper0(ScriptBytecodeAdapter.java:152)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.work(InteractiveShellRunner.groovy:124)
at org.codehaus.groovy.tools.shell.ShellRunner.run(ShellRunner.groovy:59)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.super$2$run(InteractiveShellRunner.groovy)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:132)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuper0(ScriptBytecodeAdapter.java:152)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.run(InteractiveShellRunner.groovy:83)
at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:232)
at org.apache.tinkerpop.gremlin.console.Console.(Console.groovy:166)
at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:232)
at org.apache.tinkerpop.gremlin.console.Console.main(Console.groovy:478)
gremlin>

Start with KCVSConfiguration.object2StaticBuffer and JanusGraphVariables.set, the locations shown in the stack trace. Reproduce the issue with graph.variables().set('systemAdmins', ['stephen','peter','pavel']) using the documented Graph Variables behavior. Done means list-valued graph variables are accepted instead of raising UnsupportedOperationException.

Written by the indexing model from the issue text.