utility/timer: Implement

We often need a continually ticking timer for our daemons. This utility
wraps an sd_event time source as a convenience. This is meant to be a
usable replacement for the timer.hpp found in other openbmc projects.

Tested:
    New tests pass with full coverage. Changes to the phosphor-watchdog
    that rely on this utility work as expected.

Change-Id: Id12aed9e5b018e7eca825c4a7ac7b4f46e2f04c6
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/Makefile.am b/test/Makefile.am
index 2223dfc..6cddc88 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -61,3 +61,8 @@
 source_time_SOURCES = source/time.cpp
 source_time_CPPFLAGS = $(gtest_cppflags)
 source_time_LDADD = $(gtest_ldadd)
+
+check_PROGRAMS += utility/timer
+utility_timer_SOURCES = utility/timer.cpp
+utility_timer_CPPFLAGS = $(gtest_cppflags)
+utility_timer_LDADD = $(gtest_ldadd)