Fix sys.stdin.encoding return None issue

when using "check_output" of process.py in bash script,
sys.stdin.encoding return None, not "utf-8", then
it will throw "TypeError: unicode() argument 2 must be string,
not None" error
Now this patch fix it.

Change-Id: Iecb88f68b3abe904e042a843e3e40a8a553adc8d
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1005045
Signed-off-by: hadong <hadong0720@gmail.com>