Selectively install through pip (#139)

Selectively install through pip 
* update setup.py

setup.py

@@ -29,9 +29,35 @@ def read(fname):
 
 class CustomInstallCommand(install):
     '''a customized install class in pip module'''
+    user_options = install.user_options + [
+        ('sdk-only', None, '<add --sdk-only if you want to only install nni sdk')
+    ]
+
+    def initialize_options(self):
+        install.initialize_options(self)
+        self.sdk_only = None
+
+    def install_requires(self):
+        self.install_requires_list = [
+            'astor',
+            'hyperopt',
+            'json_tricks',
+            'numpy',
+            'psutil',
+            'pyyaml',
+            'requests',
+            'scipy',
+            'schema',
+            'pyhdfs'
+        ]
+        for pkg in self.install_requires_list:
+            subprocess.run(['python3', '-m', 'pip', 'install', pkg], check=True)
+
     def run(self):
         super().run()
+        if self.sdk_only is None:
             subprocess.run(['make', 'pip-install'], check=True)
+        self.install_requires()
 
 setup(
     name = 'NNI',
@@ -52,18 +78,7 @@ setup(
     },
     package_data = {'nni': ['**/requirements.txt']},
     python_requires = '>=3.5',
-    install_requires = [
-        'astor',
-        'hyperopt',
-        'json_tricks',
-        'numpy',
-        'psutil',
-        'pyyaml',
-        'requests',
-        'scipy',
-        'schema',
-        'pyhdfs'
-    ],
+    
 
     cmdclass={
         'install': CustomInstallCommand