review(XS): 7121111: -server -Xcomp -XX:+TieredCompilation does not invoke C2 compiler

[Igor Veresov]

We should be more aggressive in tiered mode with -Xcomp and exercise C2 more. 
With this change will first compile a level 3 version, then do one invocation of it and compile a level 4 and then continue executing it. 



Webrev: http://cr.openjdk.java.net/~iveresov/7121111/webrev.00 

igor