Create common json_parser_utils functions

Create a json_parser_utils namespace containing common functions for
parsing JSON.

Extract the common functions from the JSON parsing code in the
phosphor-regulators and phosphor-power-sequencer applications.
Both applications have some identical parsing functions.

Create a common ConfigFileParserError class. The phosphor-regulators and
phosphor-power-sequencer applications both have an identical version of
this exception class.

Extract the common test cases from the two applications and put them in
a common location as well.

Summary:
* Common JSON parsing functions in
  phosphor-power-sequencer/src/config_file_parser.* and
  phosphor-regulators/src/config_file_parser.* moved to
  json_parser_utils.*
* Common test cases in
  phosphor-power-sequencer/test/config_file_parser_tests.cpp and
  phosphor-regulators/test/config_file_parser_tests.cpp moved to
  test/json_parser_utils_tests.cpp
* phosphor-power-sequencer/src/config_file_parser_error.hpp and
  phosphor-regulators/src/config_file_parser_error.hpp replaced with
  config_file_parser_error.hpp
* phosphor-power-sequencer/test/config_file_parser_error_tests.cpp and
  phosphor-regulators/test/config_file_parser_error_tests.cpp replaced
  with test/config_file_parser_error_tests.cpp

Tested:
* Ran automated test cases.

Change-Id: I35074c5e42d9e89def41ba8e729fe11c54ed8d27
Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
diff --git a/phosphor-power-sequencer/src/config_file_parser.cpp b/phosphor-power-sequencer/src/config_file_parser.cpp
index e8d68d5..07566ae 100644
--- a/phosphor-power-sequencer/src/config_file_parser.cpp
+++ b/phosphor-power-sequencer/src/config_file_parser.cpp
@@ -17,11 +17,16 @@
 #include "config_file_parser.hpp"
 
 #include "config_file_parser_error.hpp"
+#include "json_parser_utils.hpp"
 
+#include <cstdint>
 #include <exception>
 #include <fstream>
 #include <optional>
+#include <stdexcept>
 
+using namespace phosphor::power::json_parser_utils;
+using ConfigFileParserError = phosphor::power::util::ConfigFileParserError;
 using json = nlohmann::json;
 namespace fs = std::filesystem;