debugcommands: allow sending of simple commands with debugwireproto
Previously, we only had support for low-level "raw" operations.
A goal of `hg debugwireproto` is to allow easily performing
higher-level primitives, such as sending a wire protocol command
and reading its response.
We implement a "command" action that does just this.
Currently, we only support simple commands (those without payloads).
We have basic support for sending command arguments. We don't yet
support sending dictionary arguments. This will be implemented later.
To prove it works, we add tests to test-ssh-proto.t that send some
"listkeys" commands.
Note: we don't observe/report os.read() events because these may not be
deterministic. We instead observe/report the read() and readline()
operations on the bufferedinputpipe. These *should* be deterministic.
Differential Revision: https://phab.mercurial-scm.org/D2406