Psiphon in probe-engine

[bassosimone]

The Psiphon test is fully integrated inside of probe-engine making it ready for deployment.

The steps required are:

• httpx implement NewClientWithProxy (httpx: Implement NewClientWithProxy netx#130)
• HTTPDoConfig: add support for proxy function (HTTPDoConfig: add support for proxy function netx#131)
• porcelain: add proxy and byte counting support (x/logger: mimic cURL logging netx#137)
• build.sh: re-enable psiphon (ooni/probe-cli#79)
• x/logger: mimic cURL logging (x/logger: mimic cURL logging netx#137)
• psiphon: use netx so we fill the HTTP template (psiphon: use netx so we fill the HTTP template #129)
• psiphon: make sure data format matches old implementation (psiphon: make sure data format matches old implementation #128)
• psiphon: make sure we're using latest version of dependencies (psiphon: make sure we're using latest version of dependencies #141)
• orchestra: implement authenticated requests (orchestra: implement authenticated requests #148)
• psiphon: fetch config via authenticated orchestra (Fetch psiphon config via authenticated orchestra #109)
• psiphon: use config from orchestra (psiphon: use config from orchestra #167)
• orchestra: MK compatible platform names (orchestra: MK compatible platform names #169)
• orchestra: store login and tokens on persistent storage (orchestra: store authentication information #164)
• psiphon: follow-up of fetching config from orchestra (psiphon: follow-up of using config from orchestra #168)

[hellais]

@bassosimone can you add here a checklist of what are the next steps for getting this deployed?

I believe we now have the psiphon test inside of probe-engine, but building is disabled in probe-cli as we didn't want to include it for the stable release.

[bassosimone]

@hellais here's what I currently have sketched out (@bassosimone I moved the items list into the top issue ~ Arturo).

[bassosimone]

This is done!