RFR: 8029326: G1 does not check if threads gets created

[Erik Helin]

Hi all,

this change makes sure that G1 checks that an OS thread actually gets 
created when the concurrent refinement threads and the concurrent 
marking thread are created.

Webrev:
http://cr.openjdk.java.net/~ehelin/8029326/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8029326

Testing:
- JPRT
- Setting ulimit -u to a really low value and ensure that the correct
   message is printed and the VM exits gracefully during initialization

Thanks,
Erik