bug fixes for obfs4 only. test will fail due to #133

[jmwample]

Fix for unconditional return in obfs4 WrapConnection - move checks on proper data length earlier in the function and continue through loop when the MAC mark that we are looking for is not found.

The fix(es) applied in this PR relates to #132 as we add a temporary fix that creates an ioutil.tempdir for each obfs4 session ensuring separation of state. However this is probably not a good long-term fix as file descriptor limitations might cause issues, also we probably don't need any of the files to begin with.

closes #128
relates to #132

Changes

obfs4

• move mark len check proper locations
  • too short check up front
  • not found, but not past max at end for retry
• mark not found w/ one reg, continue to next instead of return
• use tempdir instead of current dir for obfs4 state

Proof that the fixes works:

TestSuccessfulWrapMulti - checks that a connection can be established for an obfs4 session even when multiple obfs4 sessions map to the same phantom address.

[jmwample]

solving failing tests will be solved in a separate PR.