[IntelliJ]Warning cannot find cluster when there is no main class, run livy interactive console

[jingyanjingyan]

Build: Develop 880

Repro Steps:

1. Make sure there is no config file
2. Open a scala file, run livy interactive console

Result:
Warning cannot find the target cluster

The config file include cluster but does not have main class actually

[jingyanjingyan]

Repro with develop 903

[jingyanjingyan]

Repro with develop 907

[jingyanjingyan]

Discuss with @wezhang , Design to:
When user click Edit, the cluster should be empty cause user haven't choose any one.

Legacy issue:
Click continue anyway, the livy interactive console does not launched and no useful warning message for it.
Expect:
Any warning message for user haven't select any cluster?

[jingyanjingyan]

Verify with build develop 914:
Click continue anyway, the livy interactive console does not launch and no useful warning message for it.

[v-jiche]

Verified. Fixed.
Build:
azure-toolkit-for-intellij-2018.3.develop.943.12-29-2018