Move TemporaryFile class to root directory

Source code that is shared across applications is located in the root
directory of the phosphor-power repository.

The TemporaryFile class was originally created for the
phosphor-regulators application.  However it is general purpose and is
now needed by the phosphor-power-sequencer application.

Move the TemporaryFile class to the root directory.  Update C++ files
that use the TemporaryFile class since it is now in a different
namespace.  Update affected meson.build files.

Change-Id: I6d18080d2436a5da87b7ab51ac003c503caa36a3
Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
diff --git a/meson.build b/meson.build
index badc8b5..da7a277 100644
--- a/meson.build
+++ b/meson.build
@@ -156,6 +156,7 @@
     error_hpp,
     'gpio.cpp',
     'pmbus.cpp',
+    'temporary_file.cpp',
     'utility.cpp',
     dependencies: [
         nlohmann_json_dep,