Fix some trivial py3 errors

Change-Id: I72334d2ca82057e591dca4fcfa9ef7ecdd3b6878
Update variable name in test_shell.py

Some variable names cannot reflect its real meaning in unit
test for heat shell, this patch update the variable names to
be more accurate.

Change-Id: Ib9b4770769a20b5e139620ceab0f463a4e035d66
Merge "Update variable name in test_shell.py"
Merge "Fix some trivial py3 errors"