Divide timeout equally between functions #1820

Description

In case test generation takes a lot of time (for instance see #1819) generation for one function may take all time provided for several functions.

To Reproduce

class NoTestsProblem:
    def __init__(self):
        self.board = []

    def set_position(self, row, col, symbol):
        self.board[row][col] = symbol
        return symbol

    def start(self):
        self.set_position(1, 2, "O")

Steps to reproduce the behavior:

1. Add python class above to existing project
2. Invoke test generation for start function only - test is generated instantly
3. Invoke test generation for both functions set_position and start

Expected behavior

Timeout for all selected functions is equally distributed between functions, so tests for both or at least start are generated.

Actual behavior

No tests are generate neither for set_position nor for start. It seems that it start generation for set_position and it takes all time due #1819.

Additional considerations

If it's possible it would be better to specify timeout for one functions, so no matter how many functions in the file test generation for each of them would take specified time.