Merge #12987: tests/tools: Enable additional Python flake8 rules for automatic linting via Travis

643aad17fa Enable additional flake8 rules (practicalswift)
f020aca297 Minor Python cleanups to make flake8 pass with the new rules enabled (practicalswift)

Pull request description:

  Enabled rules:

  ```
  * E242: tab after ','
  * E266: too many leading '#' for block comment
  * E401: multiple imports on one line
  * E402: module level import not at top of file
  * E701: multiple statements on one line (colon)
  * E901: SyntaxError: invalid syntax
  * E902: TokenError: EOF in multi-line string
  * F821: undefined name 'Foo'
  * W293: blank line contains whitespace
  * W606: 'async' and 'await' are reserved keywords starting with Python 3.7
  ```

  Note to reviewers:
  * In general we don't allow whitespace cleanups to existing code, but in order to allow for enabling Travis checking for these rules a few smaller whitespace cleanups had to made as part of this PR.
  * Use [this `?w=1` link](https://github.com/bitcoin/bitcoin/pull/12987/files?w=1) to show a diff without whitespace changes.

  Before this commit:

  ```
  $ flake8 -qq --statistics --ignore=B,C,E,F,I,N,W --select=E112,E113,E115,E116,E125,E131,E133,E223,E224,E242,E266,E271,E272,E273,E274,E275,E304,E306,E401,E402,E502,E701,E702,E703,E714,E721,E741,E742,E743,F401,E901,E902,F402,F404,F406,F407,F601,F602,F621,F622,F631,F701,F702,F703,F704,F705,F706,F707,F811,F812,F821,F822,F823,F831,F841,W292,W293,W504,W601,W602,W603,W604,W605,W606 .
  5     E266 too many leading '#' for block comment
  4     E401 multiple imports on one line
  6     E402 module level import not at top of file
  5     E701 multiple statements on one line (colon)
  1     F812 list comprehension redefines 'n' from line 159
  4     F821 undefined name 'ConnectionRefusedError'
  28    W293 blank line contains whitespace
  ```

  After this commit:

  ```
  $ flake8 -qq --statistics --ignore=B,C,E,F,I,N,W --select=E112,E113,E115,E116,E125,E131,E133,E223,E224,E242,E266,E271,E272,E273,E274,E275,E304,E306,E401,E402,E502,E701,E702,E703,E714,E721,E741,E742,E743,F401,E901,E902,F402,F404,F406,F407,F601,F602,F621,F622,F631,F701,F702,F703,F704,F705,F706,F707,F811,F812,F821,F822,F823,F831,F841,W292,W293,W504,W601,W602,W603,W604,W605,W606 .
  $
  ```

Tree-SHA512: fc7d5e752298a50d4248afc620ee2c173135b4ca008e48e02913ac968e5a24a5fd5396926047ec62f1d580d537434ccae01f249bb2f3338fa59dc630bf97ca7a

0 files changed, 0 insertions, 0 deletions