tests: use print function for python3 compatibility

and add the <BLANKLINES> where needed.

slapos/rebootstrap/different_version.txt

@@ -38,8 +38,9 @@ TODO: The test is incomplete for 2 reasons:
 ...   def __getattr__(self, attr):
 ...     return getattr(sys, attr)
 ... """)
->>> print system(buildout),
+>>> print(system(buildout))
 Develop: '/sample-buildout/recipes'
+<BLANKLINE>
 >>> write(sample_buildout, 'buildout.cfg',
 ... """
 ... [buildout]
@@ -57,7 +58,7 @@ Develop: '/sample-buildout/recipes'
 ... recipe = recipes:pyshow
 ... """ % dict(syspython=sys.executable))
 
->>> print system(buildout), # doctest: +ELLIPSIS
+>>> print(system(buildout)) # doctest: +ELLIPSIS
 slapos.rebootstrap: Make sure that the section 'installpython' won't be reinstalled after rebootstrap.
 Develop: '/sample-buildout/recipes'
 Installing installpython.
@@ -73,3 +74,4 @@ Buildout will be restarted automatically to have this change applied.
 While:
   Installing.
 Error: Couldn't find a distribution for 'setuptools==...'
+<BLANKLINE>

slapos/rebootstrap/same_version.txt

@@ -2,8 +2,9 @@ Simple case: switch to a Python with same major/minor version
 -------------------------------------------------------------
 
 >>> import sys
->>> print system(buildout),
+>>> print(system(buildout))
 Develop: '/sample-buildout/recipes'
+<BLANKLINE>
 >>> write(sample_buildout, 'buildout.cfg',
 ... """
 ... [buildout]
@@ -21,7 +22,7 @@ Develop: '/sample-buildout/recipes'
 ... recipe = recipes:pyshow
 ... """ % dict(syspython=sys.executable))
 
->>> print system(buildout),
+>>> print(system(buildout))
 slapos.rebootstrap: Make sure that the section 'installpython' won't be reinstalled after rebootstrap.
 Develop: '/sample-buildout/recipes'
 Installing installpython.
@@ -39,15 +40,17 @@ Develop: '/sample-buildout/recipes'
 Updating installpython.
 Installing realrun.
 Running with: /sample_buildout/parts/installpython/bin/python
+<BLANKLINE>
 
->>> print system(buildout),
+>>> print(system(buildout))
 Develop: '/sample-buildout/recipes'
 Updating installpython.
 Updating realrun.
 Running with: /sample_buildout/parts/installpython/bin/python
+<BLANKLINE>
 
 >>> cp(buildout + '-orig', buildout)
->>> print system(buildout),
+>>> print(system(buildout))
 slapos.rebootstrap: Make sure that the section 'installpython' won't be reinstalled after rebootstrap.
 Develop: '/sample-buildout/recipes'
 Updating installpython.
@@ -64,3 +67,4 @@ Develop: '/sample-buildout/recipes'
 Updating installpython.
 Updating realrun.
 Running with: /sample_buildout/parts/installpython/bin/python
+<BLANKLINE>

slapos/rebootstrap/same_version_already_installed.txt

@@ -3,8 +3,9 @@
 An edge case is when the python is provided by a part that does not need to install anything.
 
 >>> import sys
->>> print system(buildout),
+>>> print(system(buildout))
 Develop: '/sample-buildout/recipes'
+<BLANKLINE>
 >>> write(sample_buildout, 'buildout.cfg',
 ... """
 ... [buildout]
@@ -22,9 +23,10 @@ Develop: '/sample-buildout/recipes'
 ... recipe = recipes:pyshow
 ... """ % dict(syspython=sys.executable))
 
->>> print system(buildout),
+>>> print(system(buildout))
 Using already installed /system_python
 Develop: '/sample-buildout/recipes'
 Installing already_installed_python.
 Installing realrun.
 Running with: /system_python
+<BLANKLINE>

slapos/rebootstrap/tests.py

@@ -59,12 +59,13 @@ class Pyinstall:
   update = install
 """)
   write(sample_buildout, 'recipes', 'pyalreadyinstalled.py', """
+from __future__ import print_function
 import os, zc.buildout, shutil, sys
 
 class PyAlreadyInstalled:
 
   def __init__(self, buildout, name, options):
-    print "Using already installed", sys.executable
+    print("Using already installed", sys.executable)
     options['executable'] = sys.executable
 
   def install(self):
@@ -73,6 +74,7 @@ class PyAlreadyInstalled:
   update = install
 """)
   write(sample_buildout, 'recipes', 'pyshow.py', """
+from __future__ import print_function
 import os, zc.buildout, shutil, sys
 
 class Pyshow:
@@ -81,7 +83,7 @@ class Pyshow:
     pass
 
   def install(self):
-    print 'Running with:', sys.executable
+    print('Running with:', sys.executable)
     return []
 
   update = install