py3: replace os.environ with encoding.environ (part 2 of 5)

py3: replace os.environ with encoding.environ (part 1 of 5) os.environ is a dictionary which has string elements on Python 3. We have encoding.environ which take care of all these things. This is the first patch of 5 patch series which tend to replace the occurences of os.environ with encoding.environ as using os.environ will result in unusual behaviour.

tests: exclude bundled pywatchman from check-code test pywatchman is imported from upstream and therefore fails to pass linting. We have added 'no-check-code' manually to every file in the past. This is cumbersome and modifies upstream sources.

convert: parse perforce data on-demand We are using read-only attributes that parse the perforce data on demand. We are reading the data only once whenever an attribute is requested and use it throughout the import process. This is equivalent to the previous behavior, but we are avoiding reading from perforce when we initialize the object, but instead run it during the actual import process, when the first attribute is requested (usually getheads(), see `convertcmd.convert`).

convert: return calculated values from parse() instead of manpulating state

convert: move localname state to function scope