tests: enable alertnotify test for Windows

The semantics of "echo" are different there and they change the resulting text,
but they're still correct and predictable.
tests: allow rpc-tests to get filenames for bitcoind and bitcoin-cli from the environment

This will allow for windows tests to run with bitcoind.exe and bitcoin-cli.exe
tests: fix forknotify.py on windows

Windows interprets 'foo.txt' as a literal filename while "foo.txt" is treated
as expected.
tests: remove old pull-tester scripts

They're unused since the switch to Travis
tests: replace the old (unused since Travis) tests with new rpc test scripts
add tests to travis
Merge pull request #5185

2191eac add tests to travis (Cory Fields)
7667850 tests: replace the old (unused since Travis) tests with new rpc test scripts (Cory Fields)
fa7f8cd tests: remove old pull-tester scripts (Cory Fields)
5122ea7 tests: fix forknotify.py on windows (Cory Fields)
7a41614 tests: allow rpc-tests to get filenames for bitcoind and bitcoin-cli from the environment (Cory Fields)
f635269 tests: enable alertnotify test for Windows (Cory Fields)