This commit adds a tool for combining log files from multiple instances
of bitcoinds as well as the test_framework.log file. This gives a
combined view of what the test framework and all bitcoin instances were
doing during a qa test.
Change bumpfee tests to use the spend_one_input function instead of the
create_fund_sign_send function. The latter function would choose transaction
inputs and fees in unpredictable ways depending on the order that tests ran,
which meant that adding new tests could cause old tests to fail, and in general
made bumpfee.py fragile and unpleasant to work with.
