[land-bot] Improve error reporting when fetching revision status fails
[land-bot] Improve error reporting when fetching revision status fails

Summary:
Prior to this patch, the request can fail for a number of reasons and provide
no helpful info to investigate the issue.

Test Plan:
```
vim land-patch.sh    # edit the domain on the REVISION_STATUS line to a non-existent domain
CONDUIT_TOKEN=invalid ./land-patch --dry-run -r D5930   # Failed to connect to non-existent domain
git reset --hard <this-patch>
CONDUIT_TOKEN=invalid ./land-patch --dry-run -r D5930   # Gives Conduit error as expected
CONDUIT_TOKEN=<valid-token> ./land-patch --dry-run -r D5930   # Still errors as expected since this revision isn't accepted
```

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6143

cculianu/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,cculianu/bitcoin-abc,cculianu/bitcoin-abc,cculianu/bitcoin-abc