salt/grains : fix detection of osrelease for SmartOS
salt/grains : better detection of cpu_model on SunOS platforms

Old version only gives cpu_model on SPARC platforms, but x86
platforms shows only "x86". By using cpu_info:*:brand instead of
cpu_info:*:implementation, you will get something as :
"Intel(r) Xeon(r) CPU E5-2630 0 @ 2.30GHz"
salt/grains : add SunOS cpu_flags support

Tested on :

- SunOS 5.11 both sparc and x86

- SmartOS joyent_20130405T010449Z
Merge pull request #4991 from virtua-network/develop

salt/grains : fix detection of osrelease for SmartOS