expand nested Path argument in FileSystems requests

[jhidding]

Currently, many {...}Request messages have a Path message embedded. The Python bindings would benefit from having these path fields expanded into the filesystem and path fields.

[sverhoeven]

So replace

message Path {
    FileSystem filesystem = 1;
    // In Xenon it is of class Path
    string path = 2;
}

With

// In Xenon it is of class nl.esciencecenter.xenon.filesystems.Path
message Path {
  string path = 1;
}

message FilesystemPath {
  FileSystem filesystem = 1;
  Path path 2;
}

And replace all occurrences with Path in rpc methods with FilesystemPath.

[sverhoeven]

Currently the gprc server is using the Path(String path) constructor, which uses / as default separator.

A alternative path message type modeled after thePath(char separator, boolean isAbsolute, List<String> elements) constructor would be.

message Path {
  repeated string elements = 1;
  string separator = 2;
  bool isAbsolute = 3;
}

Then it is the responsibility of the client to deconstruct the path string into elements.

@jhidding Which Path message type is your preference?

[sverhoeven]

Has been implemented