sdbusplus: use shorter type aliases

The sdbusplus headers provide shortened aliases for many types.
Switch to using them to provide better code clarity and shorter
lines.  Possible replacements are for:
  * bus_t
  * exception_t
  * manager_t
  * match_t
  * message_t
  * object_t
  * slot_t

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I9bb7b9a430d029ddaf2a08ea26acb775b9b2b152
diff --git a/certificate.hpp b/certificate.hpp
index 4e90ea1..cb4eba6 100644
--- a/certificate.hpp
+++ b/certificate.hpp
@@ -97,7 +97,7 @@
      *  @param[in] watchPtr - watch on self signed certificate
      *  @param[in] parent - the manager that owns the certificate
      */
-    Certificate(sdbusplus::bus::bus& bus, const std::string& objPath,
+    Certificate(sdbusplus::bus_t& bus, const std::string& objPath,
                 CertificateType type, const std::string& installPath,
                 const std::string& uploadPath, Watch* watch, Manager& parent);
 
@@ -115,7 +115,7 @@
      *  @param[in] parent - Pointer to the manager which owns the constructed
      * Certificate object
      */
-    Certificate(sdbusplus::bus::bus& bus, const std::string& objPath,
+    Certificate(sdbusplus::bus_t& bus, const std::string& objPath,
                 const CertificateType& type, const std::string& installPath,
                 X509_STORE& x509Store, const std::string& pem, Watch* watchPtr,
                 Manager& parent);