Fix logic for "nova flavor-show 0#"

For perviously logic, if flavor id is
start with "0Number", int(name_or_id)
will convert it to "Number". If flavor
id "Number" exist in DB, it will show
up for query with "0Number".
This fix enter flavor search logic at
the beginning. Also add one more UT
for this function.

Change-Id: Ic48ff4275978404064c0c6fce6f98181660aa84a
Fixes: bug 1268456
Merge "Fix logic for "nova flavor-show 0#""