tests/test-check-pyflakes.t

py3: use pycompat.getcwd() instead of os.getcwd()

We have pycompat.getcwd() which returns bytes path on Python 3. This patch
changes most of the occurences of the os.getcwd() with pycompat one.

#require test-repo pyflakes hg10

  $ . "$TESTDIR/helpers-testrepo.sh"
  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate 'set:**.py or grep("^#!.*python")' \
  > -X mercurial/pycompat.py \
  > 2>/dev/null \
  > | xargs pyflakes 2>/dev/null | "$TESTDIR/filterpyflakes.py"
  contrib/python-zstandard/tests/test_data_structures.py:107: local variable 'size' is assigned to but never used
  tests/filterpyflakes.py:39: undefined name 'undefinedname'