Convert soong scripts to python 3

Except manifest_utils, which is used by
apexer.

Tests run:
m construct_context_test manifest_check_test manifest_fixer_test test_config_fixer_test
out/host/linux-x86/testcases/construct_context_test/x86_64/construct_context_test
out/host/linux-x86/testcases/manifest_check_test/x86_64/manifest_check_test
out/host/linux-x86/testcases/manifest_fixer_test/x86_64/manifest_fixer_test
out/host/linux-x86/testcases/test_config_fixer_test/x86_64/test_config_fixer_test

Bug: 203436762
Test: Tests listed above + presubmits
Change-Id: Ife75b3af1efc871a2d8521d26153a262573bb706