Use nested namespace

Nested namespace is introduced in C++ 17. This saves nearly 50 lines.
This change also puts tests into a nested namespace, which saves
unnecessary using directives.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I7c3e38588fd5c2cbd83ac13ee24327318e8c06a4
diff --git a/bmc-vmi-ca/ca_cert_entry.cpp b/bmc-vmi-ca/ca_cert_entry.cpp
index 94c0a25..f4d7b2e 100644
--- a/bmc-vmi-ca/ca_cert_entry.cpp
+++ b/bmc-vmi-ca/ca_cert_entry.cpp
@@ -4,9 +4,7 @@
 

 #include "ca_certs_manager.hpp"

 

-namespace ca

-{

-namespace cert

+namespace ca::cert

 {

 

 void Entry::delete_()

@@ -14,5 +12,4 @@
     // Remove entry D-bus object

     manager.erase(id);

 }

-} // namespace cert

-} // namespace ca

+} // namespace ca::cert