Fix requirement parser (bazelbuild#1009)

Fix requirements_parser.bzl

Space in requirement.txt should delimit options into distinct arguments.
Otherwise, `pip` would be invoked with incorrect argument containing
space.

python/pip_install/private/test/requirements_parser_tests.bzl

@@ -60,16 +60,16 @@ certifi==2021.10.8 \
 
     # Options
     asserts.equals(env, ["--pre"], parse("--pre\n").options)
-    asserts.equals(env, ["--find-links /my/local/archives"], parse("--find-links /my/local/archives\n").options)
-    asserts.equals(env, ["--pre", "--find-links /my/local/archives"], parse("""\
+    asserts.equals(env, ["--find-links", "/my/local/archives"], parse("--find-links /my/local/archives\n").options)
+    asserts.equals(env, ["--pre", "--find-links", "/my/local/archives"], parse("""\
 --pre
 --find-links /my/local/archives
 """).options)
-    asserts.equals(env, ["--pre", "--find-links /my/local/archives"], parse("""\
+    asserts.equals(env, ["--pre", "--find-links", "/my/local/archives"], parse("""\
 --pre # Comment
 --find-links /my/local/archives
 """).options)
-    asserts.equals(env, struct(requirements = [("FooProject", "FooProject==1.0.0")], options = ["--pre", "--find-links /my/local/archives"]), parse("""\
+    asserts.equals(env, struct(requirements = [("FooProject", "FooProject==1.0.0")], options = ["--pre", "--find-links", "/my/local/archives"]), parse("""\
 --pre # Comment
 FooProject==1.0.0
 --find-links /my/local/archives

python/pip_install/requirements_parser.bzl

@@ -96,6 +96,9 @@ def _handleParseDependency(input, buffer, result):
 def _handleParseOption(input, buffer, result):
     if input == "\n" and buffer.endswith("\\"):
         return (_STATE.ParseOption, buffer[0:-1])
+    elif input == " ":
+        result.options.append(buffer.rstrip("\n"))
+        return (_STATE.ParseOption, "")
     elif input == "\n" or input == EOF:
         result.options.append(buffer.rstrip("\n"))
         return (_STATE.ConsumeSpace, "")