Fix newline parsing in pgpass

[SebastienGllmt]

Previous behavior

When parsing pgpass files, the BufReader's read_line function is used which does not strip \n or \r. To handle this, a substring was created that strips out the last character (&line[..line.len() - 1])

Why is this an issue

This behavior fails in two cases:

1. If the file uses \r\n instead of just \n
2. If the file has no trailing newline

Case (2) is subtle because it means if you modify your pgpass to add a new entry and forget to add a trailing newline to your file, [..line.len() - 1] will cut off the last letter of your password (ex: hunter12 -> hunter1) giving you an authentication error.

How can we fix it?

Two options:

1. Similar to my PR, we manually strip the newline characters from the end of the string
2. We switch from the read_line to the lines method which strips the newline characters for you (I don't think this is a performance concern because pgpass files are presumably not large files)

Tests

I noticed there weren't any tests for load_password_from_file -- only for load_password_from_line. I assume it's because setup for a test on file reading is tedious and any issue would get caught integration tests. However, this means I'm not sure what you suggest for a test for this specific case. Please let me know if you're okay without a test or if you have a specific way you'd like me to set it up (or push to my branch yourself)

[abonander]

If you want to generate a file and check it in to tests/postgres/, that sounds fine. The login credentials (for testing) are hardcoded as postgres/password.

[abonander]

Just wrote a unit test combining the other test cases into a single "file", although it required a bit of modification.