Start arthas.core in debug mode failed with VirtualMachine ClassNotFoundException

[Hearen]

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

Environment

• Arthas version: 3.0.4
• Operating System version: 16.04.1-Ubuntu 2018 x86_64 x86_64 x86_64 GNU/Linux
• Java version of target JVM: jdk1.8.0_144
• Java version of JVM used to attach: jdk1.8.0_144

Steps to reproduce this issue

1. Configure the program arguments in IntelliJ with: -target-ip 127.0.0.1 -telnet-port 3658 -http-port 8563 -pid 13328 -core ~/.arthas/lib/3.0.4/arthas/arthas-core.jar -agent ~/.arthas/lib/3.0.4/arthas/arthas-agent.jar
2. Start com/taobao/arthas/core/Arthas.java in debug mode

Expected Result

start Arthas server and ready to monitor target process (13328).

Actual Result

Error as:

Connected to the target VM, address: '127.0.0.1:45671', transport: 'socket'
Disconnected from the target VM, address: '127.0.0.1:45671', transport: 'socket'
Start arthas failed, exception stack trace: 
java.lang.NoClassDefFoundError: com/sun/tools/attach/VirtualMachine
	at com.taobao.arthas.core.Arthas.attachAgent(Arthas.java:58)
	at com.taobao.arthas.core.Arthas.<init>(Arthas.java:25)
	at com.taobao.arthas.core.Arthas.main(Arthas.java:96)
Caused by: java.lang.ClassNotFoundException: com.sun.tools.attach.VirtualMachine
	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 3 more

F.Y.I

1. VirtualMachine lies here: ~/.m2/repository/org/powermock/powermock-module-javaagent/1.7.4/powermock-module-javaagent-1.7.4.jar!/com/sun/tools/attach/VirtualMachine.class
2. tried mvn clean compile in **/arthas/core but still no luck there.

@ralf0131 @hengyunabc

[hengyunabc]

#222