Add support for Mac vs. Linux sky_server builds

sky/tools/skypy/skyserver.py

Index: sky/tools/skypy/skyserver.py
diff --git a/sky/tools/skypy/skyserver.py b/sky/tools/skypy/skyserver.py
index d92b8448ec189441fb83c6c146550bd5328b0d80..d161eb0ddd458fd0ced042b0fa0b17daa13fd61a 100644
--- a/sky/tools/skypy/skyserver.py
+++ b/sky/tools/skypy/skyserver.py
@@ -6,9 +6,11 @@ import socket
 import subprocess
 import logging
 import os.path
+import platform
 
 SKYPY_PATH = os.path.dirname(os.path.abspath(__file__))
 SKY_TOOLS_PATH = os.path.dirname(SKYPY_PATH)
+SKYGO_PATH = os.path.join(SKY_TOOLS_PATH, 'skygo')
 SKY_ROOT = os.path.dirname(SKY_TOOLS_PATH)
 SRC_ROOT = os.path.dirname(SKY_ROOT)
 
@@ -26,9 +28,16 @@ class SkyServer(object):
         return sock.connect_ex(('localhost', port)) == 0
 
     @staticmethod
-    def _download_server_if_necessary():
-        subprocess.call(os.path.join(SKY_TOOLS_PATH, 'download_sky_server'))
-        return os.path.join(SRC_ROOT, 'out', 'downloads', 'sky_server')
+    def sky_server_path():
+
+        if platform.system() == 'Linux':
+            platform_dir = 'linux64'
+        elif platform.system() == 'Mac':
+            platform_dir = 'mac'
+        else:
+            assert False, 'No sky_server binary for this platform?'
+
+        return os.path.join(SKYGO_PATH, platform_dir, 'sky_server')
 
     def start(self):
         if self._port_in_use(self.port):
@@ -37,7 +46,7 @@ class SkyServer(object):
                 self.port)
             return
 
-        server_path = self._download_server_if_necessary()
+        server_path = self.sky_server_path()
         server_command = [
             server_path,
             '-t', self.configuration,