Add rescue for unsupported speed values in minitest
Add rescue for unsupported speed values in minitest

% rubocop test_interface.rb
Inspecting 1 file
.

1 file inspected, no offenses detected

Test with n3k/n9k/n9kv & n9k that discovered this problem:

ruby-2.1.1 test_interface.rb -v -n test_interface_speed_change --
1 runs, 2 assertions, 0 failures, 0 errors, 0 skips
Coverage report generated for MiniTest to /nobackup/cvanheuv/git.nu.dev.cvh/cisco-network-node-utils/tests/coverage. 0.0 / 0.0 LOC (100.0%) covered.

cisco/cisco-network-node-utils,chrisvanheuveln/cisco-network-node-utils,cisco/cisco-network-node-utils,chrisvanheuveln/cisco-network-node-utils