[cdc_rsync] Detect remote architecture (#86)

Improves ServerArch so that it can detect the remote architecture by
running uname and checking %PROCESSOR_ARCHITECTURE%. So far, only
x64 Linux and x64 Windows are supported, but in the future it is easy
to add support for others, e.g. aarch64, as well.

Before the detection is run, the remote architecture is guessed first
based on the destination. For instance, if the destination directory
starts with "C:\", it pretty much means Windows. If cdc_rsync_server
exists and runs fine, there's no need for detection.

Since also PortManager depends on the remote architecture, it has to
be adjusted as well. So far, PortManager assumeed that "local" means
Windows and "remote" means Linux. This is no longer the case for
syncing to Windows devices, so this CL adds the necessary abstractions
to PortManager.

Also refactors ArchType into a separate class in common, since it is
used now from several places. It is also expanded to handle future
changes that add support for different processor architectures, e.g.
aarch64.

common/remote_util.h

@@ -25,7 +25,7 @@
 
 namespace cdc_ft {
 
-// Utilities for executing remote commands on a gamelet through SSH.
+// Utilities for executing remote commands on a remote device through SSH.
 // Windows-only.
 class RemoteUtil {
  public:
@@ -63,8 +63,8 @@ class RemoteUtil {
   // Returns bad results for tricky strings like "C:\scp.path\scp.exe".
   static std::string ScpToSftpCommand(std::string scp_command);
 
-  // Copies |source_filepaths| to the remote folder |dest| on the gamelet using
-  // scp. If |compress| is true, compressed upload is used.
+  // Copies |source_filepaths| to the remote folder |dest| on the remove device
+  // using scp. If |compress| is true, compressed upload is used.
   absl::Status Scp(std::vector<std::string> source_filepaths,
                    const std::string& dest, bool compress);
 
@@ -86,27 +86,32 @@ class RemoteUtil {
   absl::Status Sftp(const std::string& commands,
                     const std::string& initial_local_dir, bool compress);
 
-  // Calls 'chmod |mode| |remote_path|' on the gamelet.
+  // Calls 'chmod |mode| |remote_path|' on the remote device.
   absl::Status Chmod(const std::string& mode, const std::string& remote_path,
                      bool quiet = false);
 
-  // Runs |remote_command| on the gamelet. The command must be properly escaped.
-  // |name| is the name of the command displayed in the logs.
+  // Runs |remote_command| on the remote device. The command must be properly
+  // escaped. |name| is the name of the command displayed in the logs.
   absl::Status Run(std::string remote_command, std::string name);
 
-  // Builds an SSH command that executes |remote_command| on the gamelet.
+  // Same as Run(), but captures both stdout and stderr.
+  // If |std_out| or |std_err| are nullptr, the output is not captured.
+  absl::Status RunWithCapture(std::string remote_command, std::string name,
+                              std::string* std_out, std::string* std_err);
+
+  // Builds an SSH command that executes |remote_command| on the remote device.
   ProcessStartInfo BuildProcessStartInfoForSsh(std::string remote_command);
 
-  // Builds an SSH command that runs SSH port forwarding to the gamelet, using
-  // the given |local_port| and |remote_port|.
-  // If |reverse| is true, sets up reverse port forwarding.
+  // Builds an SSH command that runs SSH port forwarding to the remote device,
+  // using the given |local_port| and |remote_port|. If |reverse| is true, sets
+  // up reverse port forwarding.
   ProcessStartInfo BuildProcessStartInfoForSshPortForward(int local_port,
                                                           int remote_port,
                                                           bool reverse);
 
-  // Builds an SSH command that executes |remote_command| on the gamelet, using
-  // port forwarding with given |local_port| and |remote_port|.
-  // If |reverse| is true, sets up reverse port forwarding.
+  // Builds an SSH command that executes |remote_command| on the remote device,
+  // using port forwarding with given |local_port| and |remote_port|. If
+  // |reverse| is true, sets up reverse port forwarding.
   ProcessStartInfo BuildProcessStartInfoForSshPortForwardAndCommand(
       int local_port, int remote_port, bool reverse,
       std::string remote_command);