travis: add itest on Windows
travis: add itest on Windows

This commit adds an integration test that runs on a Windows virtual
machine on Travis. The tests run inside of a "Git Bash" environment
which supports the same command line syntax as a proper bash but doesn't
have all the tooling installed. Some tools also behave differently on
Windows. Therefore we also have to simplify the command to upload the
logs to termbin and remove the upload to file.io on Windows because both
the find and tar command don't work as expected.

LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd