ART: Use optimizing compiler in image_test

Expose some compiler options so we can run the image test with
the optimizing compiler without running into a stack overflow.

Also allow a variable amount of threads in CreateCompilerDriver.
Use 16 as a middle ground on the host to speed up the otherwise
now slowed-down test.

Bug: 27240085
Bug: 27552475
Change-Id: I8db5055d32ae722c8f430903244faa9166cc4886
diff --git a/compiler/common_compiler_test.h b/compiler/common_compiler_test.h
index 7e0fbab..9552143 100644
--- a/compiler/common_compiler_test.h
+++ b/compiler/common_compiler_test.h
@@ -93,7 +93,7 @@
                             const char* method_name, const char* signature)
       SHARED_REQUIRES(Locks::mutator_lock_);
 
-  void CreateCompilerDriver(Compiler::Kind kind, InstructionSet isa);
+  void CreateCompilerDriver(Compiler::Kind kind, InstructionSet isa, size_t number_of_threads = 2U);
 
   void ReserveImageSpace();