Add IpmbSensor unit tests

Because everything was packed into IpmbSensor.cpp, which also included
main(), this commit breaks it up into the patterns we have in other
sensors, with <X>main.cpp containing the things for main.

While this doesn't clean up everything, it at least makes
processResponse unit testable, and adds one minor test for it.

Change-Id: I1eabf650ff635211e5b9a94816c2ffce250ed252
Signed-off-by: Ed Tanous <ed@tanous.net>
diff --git a/src/meson.build b/src/meson.build
index 429f7c5..6fb66a1 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -166,6 +166,7 @@
 if get_option('ipmb').allowed()
     executable(
         'ipmbsensor',
+        'IpmbSensorMain.cpp',
         'IpmbSensor.cpp',
         'IpmbSDRSensor.cpp',
         dependencies: [