wic: don't use dict.keys and dict.has_key

wic: don't use dict.keys and dict.has_key

Replaced calls of dict.keys and dict.has_key methods with the
'key in dict' statement. 'key in dict' is more pythonic, faster
and readable. dict.has_key doesn't exist in Python 3.

[YOCTO #9412]

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>