This test has failed numerous times on Travis CI. Fixes to make this
test more reliable: create the does-not-exist.dat file atomically, and
increase wait time after starting bro in order to give all input
streams a chance to try to read the input file.
Also added the input stream name to the test output, in order to make
output easier to understand if the test fails again.
The changes are now a bit more succinct with less code changes required.
Behavior is tested a little bit more thoroughly and a memory problem
when reading incomplete lines was fixed. ReadHeader also always directly
returns if header reading failed.
Error messages now are back to what they were before the change, if the
new behavior is not used.
I also tweaked the documentation text a bit.
By default, the ASCII reader does not fail on errors anymore.
If there is a problem parsing a line, a reporter warning is
written and parsing continues. If the file is missing or can't
be read, the input thread just tries again on the next heartbeat.
Options have been added to recreate the previous behavior...
const InputAscii::fail_on_invalid_lines: bool;
and
const InputAscii::fail_on_file_problem: bool;
They are both set to `F` by default which makes the input readers
resilient to failure.
