wic: code cleanup: wildcard imports

Here is what PEP8(Style Guide for Python Code) says about this:

Wildcard imports (from <module> import *) should be avoided, as they
make it unclear which names are present in the namespace, confusing
both readers and many automated tools.

(From OE-Core rev: 13416c1941f5dc8abcdb0073f2104a89eae2d6f1)

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

scripts/lib/wic/plugins/source/rootfs.py

@@ -27,14 +27,9 @@
 
 import os
 
-from wic import kickstart, msger
-from wic.utils import misc, fs_related, errors, runner, cmdln
-from wic.conf import configmgr
-from wic.plugin import pluginmgr
-import wic.imager.direct as direct
+from wic import msger
 from wic.pluginbase import SourcePlugin
-from wic.utils.oe.misc import *
-from wic.imager.direct import DirectImageCreator
+from wic.utils.oe.misc import find_bitbake_env_lines, find_artifact
 
 class RootfsPlugin(SourcePlugin):
     name = 'rootfs'