db: Notify user if deleted DB entry didn't exist.

Currently, if using the CLI to delete a DB entry,
"Database entry removed" is always returned,
regardless of whether or not the entry actually
existed in the first place. This meant that users
were never told if entries did not exist.

The same issue occurs if trying to delete a DB key
using AMI.

To address this, new API is added that is more stringent
in deleting values from AstDB, which will not return
success if the value did not exist in the first place,
and will print out specific error details if available.

ASTERISK-30001 #close

Change-Id: Ic84e3eddcd66c7a6ed7fea91cdfd402568378b18

include/asterisk/astdb.h

@@ -56,6 +56,17 @@ int ast_db_put(const char *family, const char *key, const char *value);
 /*! \brief Delete entry in astdb */
 int ast_db_del(const char *family, const char *key);
 
+/*! \brief Same as ast_db_del, but with more stringent error checking
+ *
+ * \details
+ * Unlike ast_db_del, if the key does not exist in the first place,
+ * an error is emitted and -1 is returned.
+ *
+ * \retval -1 An error occured (including key not found to begin with)
+ * \retval 0 Successfully deleted
+ */
+int ast_db_del2(const char *family, const char *key);
+
 /*!
  * \brief Delete one or more entries in astdb
  *