Collect all necessary system paths for import other modules

[tamarinvs19]

Description

Now sys.path contains path to testing file and paths to all imported modules. Due to this we can generate test if function uses import from another file.

Fixes #1562

Type of Change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Manual Scenario

1. Create module (directory) mod1
2. Create two files mod1/a.py, mod1/b.py
3. Put this code:

# file a
def sum(a, b):
    return a + b

#-------------------------------------------------
# file b
import a  # not <from mod1 import a>


def double_sum(n):
    return a.sum(n, n)

4. Try to generate tests for double_sum function

Possible result

Checklist (remove irrelevant options):

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• No new warnings
• All tests pass locally with my changes