test case updated: Testcase_Mediakit_ISO_Size

[Kamil Paral]

I have started a review of all our test cases, I'll announce here if I do some large scale changes so people can peer review if they want.

The first change is in Testcase_Mediakit_ISO_Size:
https://fedoraproject.org/w/index.php?title=QA%3ATestcase_Mediakit_ISO_Size&diff=307584&oldid=300485

I also moved it to General Tests section in the install matrix, because it is easy to be tested all at once and we don't need to have it three times on that page:
https://fedoraproject.org/w/index.php?title=QA%3AFedora_18_Install_Results_Template&diff=307603&oldid=306955