Fix handling of double quotes (MI)

Summary:
* Clean CMICmdArgValString::Validate: now it's based on CMIUtilString::SplitConsiderQuotes method:
A bit of introduction:
# Command line is wrapped into CMICmdArgContext.
# CMICmdArgSet is a set of arguments to be parsed. This class contains CMICmdArgContext as a private member.
# MI command is class which is inhereted from CMICmdBase. It contains CMICmdArgSet as a private member.

When command is executed CMICmdBase::ParseArgs() is called. This method adds args for parsing using CMICmdArgSet::Add(). Then CMICmdBase::ParseValidateCmdOptions() is called, which calls CMICmdArgSet::Validate(). Then it gets a number of arguments (using SplitConsiderQuotes().array_length) and for each arguments registered in ParseArgs() tries to validate it using CMICmdArgValBase::Validate(). Every user commands parses this string again (first time it was made in SplitConsiderQuotes) and in case of CMICmdArgValString it was made incorrectly. It searches the first and last quotes (but it should be first and next after first). Besides, it was splitted into 4 cases. 
I'm just using SplitConsiderQuotes directly, and I don't split them by hand again. 

Actually, I think we should do so in every CMICmdArgVal_XXX::Validate() method.

* Enable MiInterpreterExecTestCase.test_lldbmi_target_create test
* Fix MiExecTestCase.test_lldbmi_exec_arguments_set test

All tests pass on OS X.

Reviewers: abidh, emaste, zturner, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits, zturner, emaste, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D7860

llvm-svn: 230654