MXS-1662: Move mxs_crypt into utils

Moved the mxs_crypt function into utils and renamed to mxs::crypt (no C
code used it).

include/maxscale/utils.hh

@@ -557,6 +557,16 @@ uint64_t get_byteN(const uint8_t* ptr, int bytes);
  */
 uint8_t* set_byteN(uint8_t* ptr, uint64_t value, int bytes);
 
+/**
+ * C++ wrapper function for the `crypt` password hashing
+ *
+ * @param password Password to hash
+ * @param salt     Salt to use (see man crypt)
+ *
+ * @return The hashed password
+ */
+std::string crypt(const std::string& password, const std::string& salt);
+
 /**
  * Get kernel version
  *