[molecule] rewrite molecule.utils.exec_cmd() to not use shell=True

The following changes were required code-wide:
- use shlex.split() to split commands read from spec files
- use glob.glob() where required
- write command splitter function and make use of it instead of
  simple string splitter

molecule/specs/skel.py

@@ -17,7 +17,9 @@
 #    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 
 import os
-from molecule.compat import convert_to_unicode
+import shlex
+
+from molecule.compat import convert_to_unicode, convert_to_rawstring
 import molecule.utils
 
 class GenericSpecFunctions(object):
@@ -53,6 +55,10 @@ class GenericSpecFunctions(object):
     def ve_string_splitter(self, x):
         return convert_to_unicode(x).strip().split()
 
+    def ve_command_splitter(self, x):
+        return [convert_to_unicode(y) for y in \
+            shlex.split(convert_to_rawstring(x))]
+
     def ve_integer_converter(self, x):
         return int(x)
 

molecule/utils.py

@@ -78,9 +78,7 @@ def is_exec_available(exec_name):
     return False
 
 def exec_cmd(args, env = None):
-    # do not use Popen otherwise it will try to replace
-    # wildcards automatically ==> rsync no workie
-    return subprocess.call(' '.join(args), shell = True, env = env)
+    return subprocess.call(args, env = env)
 
 def exec_cmd_get_status_output(args):
     """Return (status, output) of executing cmd in a shell."""