Deprecate -m/+m dotest options in favor of test categories

Summary:
This change deprecates -m/+m dotest options (the options are still recognized but they print an
error message pointing to the new options) and adds a new lldb-mi test category instead. To just
run lldb-mi tests, use '-G lldb-mi'. To skip lldb-mi tests, use '--skip-category lldb-mi'. All
lldb-mi tests are marked as such using the getCategories method on the base MiTestCaseBase class
and the @lldbmi_test decorator is not needed. In case one still needs to annotate a specific test
function as an lldb-mi test, one can use the @add_test_categories(['lldb-mi']) decorator to
achieve that.

Reviewers: tfiala, dawn, ki.stfu, abidh

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D14060

llvm-svn: 251400