Add Attn config option for clearing Attn Interrupts

Added attn config option
Added UT for attn config object
Added UT for cli that uses attn config object

Signed-off-by: austinfcui <austinfcui@gmail.com>
Change-Id: I0e30ebf4d94de676814bf5e173691c4d1ee362cb
diff --git a/attn/attn_config.cpp b/attn/attn_config.cpp
index eae96f9..98ec388 100644
--- a/attn/attn_config.cpp
+++ b/attn/attn_config.cpp
@@ -29,6 +29,7 @@
     iv_flags.set(enCheckstop);
     iv_flags.set(enTerminate);
     iv_flags.set(enBreakpoints);
+    iv_flags.set(enClrAttnIntr);
 }
 
 /** @brief Clear configuration flag */
@@ -44,6 +45,7 @@
     iv_flags.reset(enCheckstop);
     iv_flags.reset(enTerminate);
     iv_flags.reset(enBreakpoints);
+    iv_flags.reset(enClrAttnIntr);
 }
 
 } // namespace attn