Proper error import & lib autodetection

[vintozver]

Move errors out to the separate module to be able to catch the import level errors

Autodetect lib dirs and import xtables

[ldx]

@vintozver the tests on Travis failed, can you take a look?

[vintozver]

stdin=subprocess.DEVNULL, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL, universal_newlines=True
AttributeError: 'module' object has no attribute 'DEVNULL'

will fix now

[coveralls]

Coverage increased (+0.02%) to 59.412% when pulling 971c44d on vintozver:master into b722987 on ldx:master.

[vintozver]

tests are now passing, sorry for the mess :)

[ldx]

Thanks!