MXS-2253 Add MXS_MODULE_PARAM_DURATION

Added a new module parameter type to be used for parameters
that specify a duration. With the suffixes 'h', 'm', 's' and
'ms' the duration can be specified in hours, minutes, seconds
or milliseconds, respectively.

Irrespective of how the duration is specified, it is always
returned as milliseconds.

For backward compatibility, when a duration value is read it must
be specifed how a value *not* defined using a suffix should be
interpreted; as seconds or milliseconds.

  value = param->get_duration(name, mxs::config::INTERPRET_AS_SECONDS);

server/core/internal/config.hh

@@ -219,6 +219,25 @@ bool is_normal_server_parameter(const char* param);
  */
 bool get_suffixed_size(const char* value, uint64_t* dest);
 
+/**
+ * Converts a string into a duration, intepreting in a case-insensitive manner
+ * an 'h'-suffix to indicate hours, an 'm'-suffix to indicate minutes, an
+ * 's'-suffix to indicate seconds and an 'ms'-suffix to indicate milliseconds.
+ *
+ * @param zValue          A numerical string, possibly suffixed by 'h', 'm',
+ *                        's' or 'ms'.
+ * @param interpretation  How a value lacking a specific suffix should be interpreted.
+ * @param pDuration       Pointer, if non-NULL, where the result is stored.
+ * @param pUnit           Pointer, if non-NULL, where the detected unit is stored.
+ *
+ * @return True on success, false on invalid input in which case @c pUnit and
+ *         @c pDuration will not be modified.
+ */
+bool get_suffixed_duration(const char* zValue,
+                           mxs::config::DurationInterpretation interpretation,
+                           std::chrono::milliseconds* pDuration,
+                           mxs::config::DurationUnit* pUnit = nullptr);
+
 // Dump a parameter list into a file as `key=value` pairs
 void dump_param_list(int file,
                      MXS_CONFIG_PARAMETER* list,