Fix various pylint 1.5.4 warnings

+ DUTSetup.py:424 Else clause on loop without a break statement
+ InterfaceUtil.py:400 Else clause on loop without a break statement
+ QemuUtils.py:564 Wrong continued indentation
+ SetupDPDKTest.py: Locally enabling broad-except
+ VatExecutor.py: Catching too general exception Exception
+ ssh.py:95 No exception type(s) specified.
+ HTTPRequest.py: Tolerate HTTPCodes.OK
+ multiple: Drop ":returns: None" from docstrings.

There are still several warnings present:
- R0902(too-many-instance-attributes)
- R0912(too-many-branches)
- R0913(too-many-arguments)
- R0914(too-many-locals)
- R0915(too-many-statements)
- R0401(cyclic-import)

And there are multiple blocks of similar lines,
mainly across various Setup*Test.py files:
- R0801(duplicate-code)

Change-Id: I582575cb52b85d69d268e6374852f6e74bb71052
Signed-off-by: Vratko Polak <vrpolak@cisco.com>