Python compat - no explicit reference to Python version

Update documentation and shebang.

Differential Revision: https://reviews.llvm.org/D56252

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350327 91177308-0d34-0410-b5e6-96231b3b80d8

docs/TestSuiteGuide.md

@@ -17,7 +17,7 @@ Quickstart
 
    ```bash
    % mkdir venv
-   % virtualenv -p python2.7 venv
+   % virtualenv venv
    % . venv/bin/activate
    % pip install svn+http://llvm.org/svn/llvm-project/llvm/trunk/utils/lit
    % lit --version

tools/opt-viewer/opt-diff.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 

tools/opt-viewer/opt-stats.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 

tools/opt-viewer/opt-viewer.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 

tools/opt-viewer/optrecord.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 from __future__ import print_function
 

utils/update_analyze_test_checks.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A script to generate FileCheck statements for 'opt' analysis tests.
 

utils/update_llc_test_checks.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A test case update script.
 

utils/update_mca_test_checks.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A test case update script.
 

utils/update_test_checks.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A script to generate FileCheck statements for 'opt' regression tests.