[analyzer] Enable subcheckers to possess checker options

Under the term "subchecker", I mean checkers that do not have a checker class on
their own, like unix.MallocChecker to unix.DynamicMemoryModeling.

Since a checker object was required in order to retrieve checker options,
subcheckers couldn't possess options on their own.

This patch is also an excuse to change the argument order of getChecker*Option,
it always bothered me, now it resembles the actual command line argument
(checkername:option=value).

Differential Revision: https://reviews.llvm.org/D57579

llvm-svn: 355297