Fix Fibre Channel attach for single WWN

The code allowed for only a string of the WWN or a list of them.
Unfortunately unicode is also returned, for which the attach fails.
This patch allows for unicode as well.

Change-Id: I4d2809b41b24b2240e447a5c09f14e6438304cd6
Fixes: bug 1214413
Update Brick to use executor

modify existing modules in Brick
to make use of the Executor object,
so we don't replicated the same
set_execute() method everywhere.

Change-Id: Ib0363029557253ad86bae90e1db4fefd24a42df7
Merge "Update Brick to use executor"
Merge "Fix Fibre Channel attach for single WWN"