Add function setRNGSeed and seed setup in python tests

modules/core/include/opencv2/core.hpp

@@ -2170,6 +2170,14 @@ is much faster to use this function to retrieve the generator and then use RNG::
 */
 CV_EXPORTS RNG& theRNG();
 
+/** @brief Sets state of default random number generator.
+
+The function sets state of default random number generator to custom value.
+@param new state for default random number generator
+@sa RNG, randu, randn
+*/
+CV_EXPORTS_W void setRNGSeed(int seed);
+
 /** @brief Generates a single uniformly-distributed random number or an array of random numbers.
 
 Non-template variant of the function fills the matrix dst with uniformly-distributed