R1:cf61f0e32dd1

Adding an "ssh" client for conduit

Summary: ..."ssh" is in quotes 'cuz this is step 1 and there's no ssh in sight
at the moment.

Test Plan:
ran api.php PHID-USER-xee4ju2teq7mflitwfcs differential.query a few times...
- tried valid input, it worked!
- tried bad input, it worked in that it failed and told me so!
ran api.php crap_user differential.query a few times...
- verified error message with respect to crap_user
ran api.php PHID-USER-xee4ju2teq7mflitwfcs crap_method a few times...
- verified error…