createiso: Use correct python version

On some systems we need to use python3, in other places it can be
another version. Instead of guessing, let's look at shebang line in
lorax executable and use the same.

JIRA: COMPOSE-2852
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/createiso.py

@@ -35,7 +35,7 @@ def emit(f, cmd):
 
 
 FIND_TEMPLATE_SNIPPET = """
-if ! TEMPLATE="$(python3 -c 'import pylorax; print(pylorax.find_templates())')"; then
+if ! TEMPLATE="$($(head -n1 $(which lorax) | cut -c3-) -c 'import pylorax; print(pylorax.find_templates())')"; then
   TEMPLATE=/usr/share/lorax;
 fi
 """.replace('\n', '')

pungi/phases/createiso.py

@@ -258,7 +258,7 @@ def run_createiso_command(runroot, num, compose, bootable, arch, cmd, mounts,
             packages.append('jigdo')
         if bootable:
             extra_packages = {
-                'lorax': ['lorax'],
+                'lorax': ['lorax', 'which'],
                 'buildinstall': ['anaconda'],
             }
             packages.extend(extra_packages[compose.conf["buildinstall_method"]])

tests/test_createiso_phase.py

@@ -448,7 +448,7 @@ class CreateisoThreadTest(helpers.PungiTestCase):
                          [mock.call('f25-build', 'x86_64', cmd['cmd'], channel=None,
                                     mounts=[self.topdir],
                                     packages=['coreutils', 'genisoimage', 'isomd5sum',
-                                              'jigdo', 'lorax'],
+                                              'jigdo', 'lorax', 'which'],
                                     task_id=True, use_shell=True, weight=None)])
         self.assertEqual(
             run_runroot.call_args_list,