Use bash-style test for Fedora version

Old-style test fails on Ubuntu when python3 enabled, with:

.../devstack/inc/python: line 52: [: 16.04: integer expression expected

Use bash-style test, which doesn't attempt to evaluate the RHS if the
LHS evaluates to false

Change-Id: If18031ab98c9060e5825c3a8d3c647bd3705cd9c
Closes-Bug: #1796174
1 file changed