http api not support vmtool command

[feixueck]

• I have searched the issues of this repository and believe that this is not a duplicate.

Environment

• Arthas version: 1.8
• Operating System version: all
• Java version of target JVM: 1.8
• Java version of JVM used to attach: 1.8

Steps to reproduce this issue

1. attach arthas to a running jvm ,and export 8563 port .
2. http api post command "vmtool --action getInstances --className java.lang.String"

Expected Result

expect get : String instances info

Actual Result

{"body":{"command":"vmtool --action getInstances --className java.lang.String","jobId":1,"jobStatus":"TERMINATED","results":[{"jobId":1,"statusCode":0,"type":"status"}],"timeExpired":false},"sessionId":"1b979c28-cd91-4e86-92e3-3a596ac58ce1","state":"SUCCEEDED"}