execution_command are running too slow

when adding a service, this two interfaces will be requested 4 or 5 times each: 

• POST http://ip:port/api/v1/stacks/SEA/versions/0.1/recommendations
• POST http:// ip:port /api/v1/stacks/SEA/versions/0.1/validations

first interface costs about 38s, second interface cost about 34s, they both call method StackAdvisorCommand.invoke(xxx), a synchronized function.

when changing Components configurations the two inteferfaces are also be requested.
the above two interfaces make the UI too slow.