internal/gomote: align golangbuild's and buildlet's work directory

golangbuild already assumes it's running in the workdir, but buildlet
creates another workdir in golangbuild's workdir's tmp directory. This
means the checkout of x/ repos ends up in a different directory than
expected, not the work directory buildlet assumes.

Set the workdir for buildlet explicitly in the golangbuild case to match
golangbuild's expectations. This means users will be dropped into a
directory with a whole bunch of stuff, like the tools they need (already
in PATH, but sometimes useful) and whatever repo they wanted checked
out for them.

Change-Id: I7ee3ba9f08cb23b3abc571b7a60b534112c5cca9
Reviewed-on: https://go-review.googlesource.com/c/build/+/615956
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Michael Knyszek <[email protected]>

internal/gomote/swarming.go

@@ -1033,7 +1033,7 @@ if __name__ == "__main__":
         os.remove(buildlet_path)
     urllib.request.urlretrieve("https://storage.googleapis.com/go-builder-data/buildlet.%s-%s", buildlet_path)
     make_executable(os.getcwd() + sep + buildlet_file)
-    subprocess.run(["%s", buildlet_path, "--coordinator=gomotessh.golang.org:443", "--reverse-type=swarming-task", "-swarming-bot", "-halt=false"], shell=False, env=os.environ.copy())
+    subprocess.run(["%s", buildlet_path, "--workdir=.", "--coordinator=gomotessh.golang.org:443", "--reverse-type=swarming-task", "-swarming-bot", "-halt=false"], shell=False, env=os.environ.copy())
 `
 	return fmt.Sprintf(cmd, goos, goarch, golangbuildBin)
 }