Use common name convention for pytest files

Use common name convention for pytest files

It is better to use consistent file names to avoid issue with sorting
etc.

Using underscore in filenames as opposed to dash was chosen because it
seems more common in pytest/python to use underscore for filenames.

Also rename the bin/tests/system/timeouts/tests-tcp.py file to
bin/tests/system/timeouts/tests_tcp_timeouts.py to avoid pytest name
collision (there can't be two files named tests_tcp.py).

(cherry picked from commit f6409ee6ac5913c6f90545a44c4346945d911162)