Create regulators StubAction class

Created the StubAction class to aid in unit testing the
phosphor-regulators application.  This simple 'stub' will either return
a predefined return value or throw a predefined exception.

Updated the meson.build file to search for includes in the test
tree.  This is where stub classes will be located.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I78030d29f3bc6a94db998c5a1712a3b4a03c3e90
diff --git a/phosphor-regulators/test/meson.build b/phosphor-regulators/test/meson.build
index fdf8c00..ee880f0 100644
--- a/phosphor-regulators/test/meson.build
+++ b/phosphor-regulators/test/meson.build
@@ -1,3 +1,8 @@
+phosphor_regulators_tests_include_directories = include_directories(
+    '.',
+    'actions'
+)
+
 test('phosphor-regulators-tests',
      executable('phosphor-regulators-tests',
                 'device_tests.cpp',
@@ -9,7 +14,10 @@
                     gtest,
                 ],
                 implicit_include_directories: false,
-                include_directories: phosphor_regulators_includes,
+                include_directories: [
+                    phosphor_regulators_include_directories,
+                    phosphor_regulators_tests_include_directories
+                ]
      )
 )