Convert rospy Time difference to seconds to compare with a timeout value

[ashishraste]

Hi UUV simulator authors,

Thanks for this amazing work!

Could you please review this pull request on the issue below?

Issue: Comparing two rospy Time instances, in thruster-allocator, doesn't produce an appropriate duration when comparing with a configurable timeout value. Error thrown:

TypeError: Cannot compare to non-Duration

Fix: This fix converts the Time difference to seconds so as to have a valid comparison with a timeout value.

[ashishraste]

Hi @awesomebytes,

Thanks for the review. Will have to wait for the maintainers approval I assume before this gets merged.