Change par file generate rules.

Make sure the shebang of the par file is consistent with the main python
script rather than use /usr/bin/python arbitrarily.

Bug: 185399398
Bug: 185094069
Test: m atest ; atest-dev --help
      m atest-py2 ; atest-py2-dev --help
Change-Id: Ice4590b3d173e6d11e608c2ca29b297df0dc4089

python/builder.go

@@ -45,7 +45,7 @@ var (
 	hostPar = pctx.AndroidStaticRule("hostPar",
 		blueprint.RuleParams{
 			Command: `sed -e 's/%interpreter%/$interp/g' -e 's/%main%/$main/g' $template > $stub && ` +
-				`echo "#!/usr/bin/env python" >${out}.prefix &&` +
+				`echo "#!/usr/bin/env $interp" >${out}.prefix &&` +
 				`$mergeParCmd -p --prefix ${out}.prefix -pm $stub $out $srcsZips && ` +
 				`chmod +x $out && (rm -f $stub; rm -f ${out}.prefix)`,
 			CommandDeps: []string{"$mergeParCmd"},

python/scripts/stub_template_host.txt

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env '%interpreter%'
 
 import os
 import re
@@ -82,7 +82,7 @@ def Main():
 
     sys.stdout.flush()
     retCode = subprocess.call(args)
-    exit(retCode)
+    sys.exit(retCode)
   except:
     raise
   finally: