[feat] Raise an exception when pip fails

Before this, sys.exit(1) was called to terminate the program directly.

src/zc/buildout/easy_install.py

@@ -1718,15 +1718,7 @@ def call_pip_wheel(spec, dest):
 
     sys.stdout.flush() # We want any pending output first
 
-    exit_code = subprocess.call(list(args), env=env)
-
-    if exit_code:
-        logger.error(
-            "An error occurred when trying to install %s. "
-            "Look above this message for any errors that "
-            "were output by pip install.",
-            spec)
-        sys.exit(1)
+    subprocess.check_call(list(args), env=env)
 
     entries = os.listdir(dest)
     try: